Basis of Presentation - Additional Information (Detail)	Mar. 31, 2013	Dec. 31, 2012	Dec. 30, 2012	Apr. 24, 2012	Mar. 31, 2012	Oct. 26, 2011
Basis Of Presentation [Line Items]
Number of financial centers	56
Consolidation of bank charters description			Eleven bank charters into one charter
Stock repurchase program, number of shares authorized to be repurchased						750,000
Common stock, shares authorized	80,000,000	80,000,000		80,000,000	80,000,000
Subsidiary of Common Parent [Member]
Basis Of Presentation [Line Items]
Number of financial centers	6
Abilene [Member]
Basis Of Presentation [Line Items]
Number of financial centers	11
Abilene [Member] | Subsidiary of Common Parent [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Cleburne [Member]
Basis Of Presentation [Line Items]
Number of financial centers	2
Stephenville [Member]
Basis Of Presentation [Line Items]
Number of financial centers	2
Stephenville [Member] | Subsidiary of Common Parent [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Granbury [Member]
Basis Of Presentation [Line Items]
Number of financial centers	2
San Angelo [Member]
Basis Of Presentation [Line Items]
Number of financial centers	3
San Angelo [Member] | Subsidiary of Common Parent [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Weatherford [Member]
Basis Of Presentation [Line Items]
Number of financial centers	3
Mineral Wells [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Hereford [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Sweetwater [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Sweetwater [Member] | Subsidiary of Common Parent [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Eastland [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Ranger [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Rising Star [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Cisco [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Southlake [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Grapevine [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Aledo [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Willow Park [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Brock [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Alvarado [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Burleson [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Keller [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Trophy Club [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Boyd [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Bridgeport [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Decatur [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Roby [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Trent [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Merkel [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Clyde [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Moran [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Albany [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Midlothian [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Crowley [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Glen Rose [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Odessa [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Odessa [Member] | Subsidiary of Common Parent [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Waxahachie [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Acton [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Fort Worth [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Fort Worth [Member] | Subsidiary of Common Parent [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1
Huntsville [Member]
Basis Of Presentation [Line Items]
Number of financial centers	1