Aggregate Activity in Allowance For Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 20,252	$ 23,798	$ 20,227	$ 24,077
Provision for (recovery of) loan losses	276	1,141	1,422	2,731
Benefit attributable to the FDIC indemnification asset		138	(46)	341
Provision for (recovery of) loan losses charged to operations	276	1,279	1,376	3,072
Provision for loan losses recorded through the FDIC indemnification asset		(138)	46	(341)
Charge-offs	(673)	(1,785)	(2,251)	(4,001)
Recoveries	403	757	860	1,104
Net charge-offs	(270)	(1,028)	(1,391)	(2,897)
Ending balance	20,258	23,911	20,258	23,911
Allowance Excluding Purchased Credit Impaired
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	20,138	23,305	20,169	23,322
Provision for (recovery of) loan losses	276	1,216	1,366	3,068
Provision for (recovery of) loan losses charged to operations	276	1,216	1,366	3,068
Charge-offs	(673)	(1,785)	(2,251)	(4,001)
Recoveries	403	757	860	1,104
Net charge-offs	(270)	(1,028)	(1,391)	(2,897)
Ending balance	20,144	23,493	20,144	23,493
Purchased Credit Impaired
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	114	493	58	755
Provision for (recovery of) loan losses		(75)	56	(337)
Benefit attributable to the FDIC indemnification asset		138	(46)	341
Provision for (recovery of) loan losses charged to operations		63	10	4
Provision for loan losses recorded through the FDIC indemnification asset		(138)	46	(341)
Ending balance	$ 114	$ 418	$ 114	$ 418