POWER OF ATTORNEY

        Know all by these presents, that the undersigned hereby constitute and
appoint each of Jon W. Howie, Sharon A. Russell and Susan Kittrell signing
singly, the undersigned's true and lawful attorney-in-fact to:

        (1)     execute for and on behalf of the undersigned Forms 3, 4 and 5 in
        accordance with Section 16(a) of the Securities Exchange Act of 1934 and
        the rules thereunder and Schedules 13D or 13G in accordance with Section
        13(d) of the Securities Exchange Act of 1934;

        (2)     do and perform any and all acts for and on behalf of the
        undersigned which may be necessary or desirable to complete and execute
        any such Form 3, 4 or 5 or Schedule 13D or 13G, complete and execute any
        amendment or amendments thereto, and timely file such form with the
        United States Securities and Exchange Commission and any stock exchange
        or similar authority; and

        (3)     take any other action of any type whatsoever in connection with
        the foregoing which, in the opinion of such attorney-in-fact, may be of
        benefit to, in the best interest of, or legally required by, the
        undersigned, it being understood that the documents executed by such
        attorney-in-fact on behalf of the undersigned pursuant to this Power of
        Attorney shall be in such form and shall contain such terms and
        conditions as such attorney-in-fact may approve in such
        attorney-in-fact's discretion.

        The undersigned hereby grant to each such attorney-in-fact full power
and authority to do and perform any and every act and thing whatsoever
requisite, necessary, or proper to be done in the exercise of any of the rights
and powers herein granted, as fully to all intents and purposes as the
undersigned might or could do if personally present, with full power of
substitution or revocation, hereby ratifying and confirming all that such
attorney-in-fact, or such attorney in-fact's substitute or substitutes, shall
lawfully do or cause to be done by virtue of this Power of Attorney and the
rights and powers herein granted. The undersigned acknowledge that the foregoing
attorneys-in-fact, in serving in such capacity at the request of the
undersigned, are not assuming, nor is the Company assuming, any of the
undersigned's responsibilities to comply with Section 13 or Section 16 of the
Securities Exchange Act of 1934.

        The execution by the undersigned of this Power of Attorney hereby
expressly revokes and terminates any powers of attorney previously granted by
the undersigned relating to Forms 3, 4 and 5 and Schedules 13D or 13G with
respect to the undersigned's holdings of and transactions in securities issued
by the Company. This Power of Attorney shall remain in full force and effect
until the undersigned is no longer required to file Forms 3, 4 and 5 or
Schedules 13D or 13G with respect to the undersigned's holdings of and
transactions in securities issued by the Company, unless earlier revoked by the
undersigned in a signed writing delivered to the foregoing attorneys-in-fact.

        IN WITNESS WHEREOF, the undersigned have caused this Power of Attorney
to be executed as of July 18, 2012.

                                        MY/ZP EQUITY, LP

                                        By: MY/ZP GP, LLC, its General Partner

                                        /s/ Michael Young
                                        ---------------------------------------
                                        Name: Michael Young
                                        Title: Member

                                        /s/ John Zapp
                                        ---------------------------------------
                                        Name: John Zapp
                                        Title: Member