LIMITED POWER OF ATTORNEY

The undersigned, Michael J. Sheen, hereby authorizes each of Thomas T. McEntire
and Anthony Eppolito (with full power to each of them to act alone), as the
undersigned's true and lawful attorney-in-fact, with full power of substitution,
to:

(1)    prepare and sign in the name of and on behalf of the undersigned any and
all forms and reports required to be filed pursuant to Section 16 of the
Securities Exchange Act of 1934 and the rules thereunder, including, but without
limitation, Form 4-Statement of Changes of Beneficial Ownership of Securities,
and Form 5-Annual Statement of Beneficial Ownership of Securities;

(2)    perform any and all acts for and on behalf of the undersigned which may
be necessary or desirable to complete and execute any such Forms 4 or 5, or
other form or report, and timely file such form or report with the United States
Securities and Exchange Commission and any stock exchange or similar authority;
and

(3)    take any other action of any type in connection with the foregoing which,
in the opinion of the 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 Limited 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 grants to each attorney-in-fact full power and authority
to do and perform any and every act and thing whatsoever required, 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 (including appointing
substitutes for themselves, for each other and for any successor to any
attorney-in-fact hereunder) 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.

This Limited Power of Attorney shall remain in effect until the undersigned is
no longer required to file Forms 4 and 5 with respect to the undersigned's
beneficial ownership of securities, unless earlier revoked by the undersigned in
a signed and dated writing delivered to each of the foregoing attorneys-in-fact.

Executed this 6th day of February 2019.

/s/ Michael J. Sheen
__________________________________________
Name: Michael J. Sheen