Fair Value - Carrying Amount and Fair Value of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
ASSETS
Cash and cash equivalents	$ 36,904	$ 27,261	$ 27,418	$ 27,928
Securities available for sale	506,744	546,043
Trading securities	4,644	4,576
Loans held for sale	2,814	1,381
Net loans	1,785,155	1,561,061
FHLB and other equity interests	18,334	15,921
Liabilities
Deposits	(2,023,781)	(1,815,053)
Subordinated debentures	(70,620)	(20,620)
Carrying Amount [Member]
ASSETS
Cash and cash equivalents	36,904	27,261
Securities available for sale	506,744	546,043
Trading securities	4,644	4,576
Loans held for sale	2,814	1,381
Net loans	1,785,155	1,561,061
FHLB and other equity interests	18,334	15,921
Interest rate swaps	766	131
Accrued interest receivable	8,387	7,312
Liabilities
Deposits	(2,023,781)	(1,815,053)
FHLB and other borrowings	(205,202)	(220,515)
Subordinated debentures	(70,620)	(20,620)
Interest rate swaps	(1,361)	(867)
Accrued interest payable	(479)	(766)
Total Fair Value [Member]
ASSETS
Cash and cash equivalents	36,904	27,261
Securities available for sale	506,744	546,043
Trading securities	4,644	4,576
Loans held for sale	2,829	1,438
Net loans	1,783,814	1,554,502
Interest rate swaps	766	131
Accrued interest receivable	8,387	7,312
Liabilities
Deposits	(2,023,312)	(1,813,916)
FHLB and other borrowings	(204,314)	(218,808)
Subordinated debentures	(61,432)	(11,761)
Interest rate swaps	(1,361)	(867)
Accrued interest payable	(479)	(766)
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
ASSETS
Cash and cash equivalents	36,904	27,261
Securities available for sale	994	981
Trading securities	4,589	4,522
Loans held for sale	0	0
Net loans	0	0
Interest rate swaps	0	0
Accrued interest receivable	6	5
Liabilities
Deposits	(1,783,037)	(1,630,888)
FHLB and other borrowings	0	0
Subordinated debentures	0	0
Interest rate swaps	0	0
Accrued interest payable	0	(344)
Significant Other Observable Inputs (Level 2) [Member]
ASSETS
Cash and cash equivalents	0	0
Securities available for sale	504,048	541,649
Trading securities	55	54
Loans held for sale	2,829	1,438
Net loans	0	0
Interest rate swaps	766	131
Accrued interest receivable	3,105	2,875
Liabilities
Deposits	(240,275)	(183,028)
FHLB and other borrowings	(204,314)	(218,808)
Subordinated debentures	(61,432)	(11,761)
Interest rate swaps	(1,361)	(867)
Accrued interest payable	(479)	(422)
Significant Unobservable Inputs (Level 3) [Member]
ASSETS
Cash and cash equivalents	0	0
Securities available for sale	1,702	3,413
Trading securities	0	0
Loans held for sale	0	0
Net loans	1,783,814	1,554,502
Interest rate swaps	0	0
Accrued interest receivable	5,276	4,432
Liabilities
Deposits	0	0
FHLB and other borrowings	0	0
Subordinated debentures	0	0
Interest rate swaps	0	0
Accrued interest payable	$ 0	$ 0