Allowance for Loan Losses - Summary of Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	$ 48,814	$ 46,580	$ 47,911	$ 46,255
Charge-offs	(5,641)	(1,002)	(8,847)	(5,488)
Recoveries	3,528	284	4,370	5,941
Net (Charge-offs)/ Recoveries	(2,113)	(718)	(4,477)	453
Provision for loan losses	3,206	1,454	6,473	608
Balance at End of Period	49,907	47,316	49,907	47,316
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	19,018	20,733	20,164	18,921
Charge-offs	(2,361)	0	(2,738)	(2,002)
Recoveries	2,896	(154)	3,072	1,681
Net (Charge-offs)/ Recoveries	535	(154)	334	(321)
Provision for loan losses	(2,575)	(602)	(3,520)	1,377
Balance at End of Period	16,978	19,977	16,978	19,977
Commercial Construction [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	7,671	4,759	6,093	5,374
Charge-offs	(1,247)	(234)	(1,247)	(693)
Recoveries	129	0	132	140
Net (Charge-offs)/ Recoveries	(1,118)	(234)	(1,115)	(553)
Provision for loan losses	4,983	653	6,558	357
Balance at End of Period	11,536	5,178	11,536	5,178
Consumer Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	7,027	6,705	6,333	6,362
Charge-offs	(445)	(436)	(997)	(983)
Recoveries	132	48	379	272
Net (Charge-offs)/ Recoveries	(313)	(388)	(618)	(711)
Provision for loan losses	302	446	1,301	1,112
Balance at End of Period	7,016	6,763	7,016	6,763
Other Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	1,790	1,379	1,653	1,165
Charge-offs	(467)	(295)	(1,046)	(740)
Recoveries	99	75	312	284
Net (Charge-offs)/ Recoveries	(368)	(220)	(734)	(456)
Provision for loan losses	484	341	987	791
Balance at End of Period	1,906	1,500	1,906	1,500
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	13,308	13,004	13,668	14,433
Charge-offs	(1,121)	(37)	(2,819)	(1,070)
Recoveries	272	315	475	3,564
Net (Charge-offs)/ Recoveries	(849)	278	(2,344)	2,494
Provision for loan losses	12	616	1,147	(3,029)
Balance at End of Period	$ 12,471	$ 13,898	$ 12,471	$ 13,898