Loans and Allowance for Loan and Lease Losses - Summary of Activity in ALLL (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 13,029	$ 12,639	$ 12,716	$ 13,833
Charge offs	(9,049)	(881)	(9,212)	(2,353)
Recoveries	729	585	785	863
Provision	8,720	0	9,140	0
Balance at end of period	13,429	12,343	13,429	12,343
Commercial loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	8,059	7,353	6,639	7,670
Charge offs	(8,509)	(730)	(8,672)	(2,117)
Recoveries	724	582	777	857
Provision	8,429	(724)	9,959	71
Balance at end of period	8,703	6,481	8,703	6,481
Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	4,069	4,287	5,109	5,133
Charge offs	0	0	0	0
Recoveries	0	1	1	2
Provision	(241)	601	(1,282)	(246)
Balance at end of period	3,828	4,889	3,828	4,889
Land Development
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	203	120	282	296
Charge offs	0	0	0	(85)
Recoveries	0	0	0	0
Provision	23	(76)	(56)	(167)
Balance at end of period	226	44	226	44
Consumer and Single Family Mortgages
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	698	879	686	734
Charge offs	(540)	(151)	(540)	(151)
Recoveries	5	2	7	4
Provision	509	199	519	342
Balance at end of period	$ 672	$ 929	$ 672	$ 929