Allowance for Loan Losses - Investments in Loans Considered to be Impaired and Related Information on Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	$ 45,925		$ 45,925		$ 52,089
Without a related allowance, Unpaid Principal Balance	55,829		55,829		67,122
Without a related allowance recorded, Related Allowance	0		0		0
With a related allowance recorded, Recorded Investment	67		67		767
With a related allowance recorded, Unpaid Principal Balance	67		67		1,469
With a related allowance recorded, Related Allowance	55		55		97
Impaired Financing Receivable, Recorded Investment, Total	45,992		45,992		52,856
Impaired Financing Receivable, Unpaid Principal Balance, Total	55,896		55,896		68,591
Impaired Financing Receivable, Related Allowance	55		55		97
With a related allowance recorded, Average Recorded Investment	70	7,078	73	4,585
With a related allowance recorded, Interest Income Recognized	1	52	4	57
Without a related allowance recorded, Average Recorded Investment	46,121	56,720	46,627	65,429
Without a related allowance recorded, Interest Income Recognized	381	500	1,170	1,501
Impaired Financing Receivable, Average Recorded Investment, Total	46,191	63,798	46,700	70,014
Impaired Financing Receivable, Interest Income Recognized, Total	382	552	1,174	1,558
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	21,028		21,028		26,968
Without a related allowance, Unpaid Principal Balance	26,366		26,366		35,474
Without a related allowance recorded, Related Allowance	0		0		0
With a related allowance recorded, Recorded Investment	0		0		0
With a related allowance recorded, Unpaid Principal Balance	0		0		0
With a related allowance recorded, Related Allowance	0		0		0
Impaired Financing Receivable, Recorded Investment, Total	21,028		21,028		26,968
Impaired Financing Receivable, Unpaid Principal Balance, Total	26,366		26,366		35,474
Impaired Financing Receivable, Related Allowance	0		0		0
With a related allowance recorded, Average Recorded Investment	0	1,014	0	2,526
With a related allowance recorded, Interest Income Recognized	0	0	0	5
Without a related allowance recorded, Average Recorded Investment	21,110	27,489	21,593	29,951
Without a related allowance recorded, Interest Income Recognized	159	271	512	330
Impaired Financing Receivable, Average Recorded Investment, Total	21,110	28,503	21,593	32,477
Impaired Financing Receivable, Interest Income Recognized, Total	159	271	512	335
Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	9,643		9,643		9,580
Without a related allowance, Unpaid Principal Balance	9,964		9,964		9,703
Without a related allowance recorded, Related Allowance	0		0		0
With a related allowance recorded, Recorded Investment	0		0		0
With a related allowance recorded, Unpaid Principal Balance	0		0		0
With a related allowance recorded, Related Allowance	0		0		0
Impaired Financing Receivable, Recorded Investment, Total	9,643		9,643		9,580
Impaired Financing Receivable, Unpaid Principal Balance, Total	9,964		9,964		9,703
Impaired Financing Receivable, Related Allowance	0		0		0
With a related allowance recorded, Average Recorded Investment	0	0	0	0
With a related allowance recorded, Interest Income Recognized	0	0	0	0
Without a related allowance recorded, Average Recorded Investment	9,702	10,995	9,477	11,964
Without a related allowance recorded, Interest Income Recognized	63	68	177	203
Impaired Financing Receivable, Average Recorded Investment, Total	9,702	10,995	9,477	11,964
Impaired Financing Receivable, Interest Income Recognized, Total	63	68	177	203
Commercial Construction [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	8,143		8,143		7,391
Without a related allowance, Unpaid Principal Balance	11,831		11,831		12,353
Without a related allowance recorded, Related Allowance	0		0		0
With a related allowance recorded, Recorded Investment	0		0		681
With a related allowance recorded, Unpaid Principal Balance	0		0		1,383
With a related allowance recorded, Related Allowance	0		0		25
Impaired Financing Receivable, Recorded Investment, Total	8,143		8,143		8,072
Impaired Financing Receivable, Unpaid Principal Balance, Total	11,831		11,831		13,736
Impaired Financing Receivable, Related Allowance	0		0		25
With a related allowance recorded, Average Recorded Investment	0	5,929	0	1,976
With a related allowance recorded, Interest Income Recognized	0	49	0	49
Without a related allowance recorded, Average Recorded Investment	8,160	9,768	8,254	14,492
Without a related allowance recorded, Interest Income Recognized	58	46	172	271
Impaired Financing Receivable, Average Recorded Investment, Total	8,160	15,697	8,254	16,468
Impaired Financing Receivable, Interest Income Recognized, Total	58	95	172	320
Consumer Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	7,000		7,000		8,026
Without a related allowance, Unpaid Principal Balance	7,553		7,553		9,464
Without a related allowance recorded, Related Allowance	0		0		0
With a related allowance recorded, Recorded Investment	45		45		53
With a related allowance recorded, Unpaid Principal Balance	45		45		53
With a related allowance recorded, Related Allowance	45		45		53
Impaired Financing Receivable, Recorded Investment, Total	7,045		7,045		8,079
Impaired Financing Receivable, Unpaid Principal Balance, Total	7,598		7,598		9,517
Impaired Financing Receivable, Related Allowance	45		45		53
With a related allowance recorded, Average Recorded Investment	47	100	49	62
With a related allowance recorded, Interest Income Recognized	1	2	2	0
Without a related allowance recorded, Average Recorded Investment	7,034	8,349	7,181	8,912
Without a related allowance recorded, Interest Income Recognized	100	114	306	693
Impaired Financing Receivable, Average Recorded Investment, Total	7,081	8,449	7,230	8,974
Impaired Financing Receivable, Interest Income Recognized, Total	101	116	308	693
Other Consumer [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	111		111		124
Without a related allowance, Unpaid Principal Balance	115		115		128
Without a related allowance recorded, Related Allowance	0		0		0
With a related allowance recorded, Recorded Investment	22		22		33
With a related allowance recorded, Unpaid Principal Balance	22		22		33
With a related allowance recorded, Related Allowance	10		10		19
Impaired Financing Receivable, Recorded Investment, Total	133		133		157
Impaired Financing Receivable, Unpaid Principal Balance, Total	137		137		161
Impaired Financing Receivable, Related Allowance	10		10		19
With a related allowance recorded, Average Recorded Investment	23	35	24	21
With a related allowance recorded, Interest Income Recognized	0	1	2	3
Without a related allowance recorded, Average Recorded Investment	115	119	122	110
Without a related allowance recorded, Interest Income Recognized	1	1	3	4
Impaired Financing Receivable, Average Recorded Investment, Total	138	154	146	131
Impaired Financing Receivable, Interest Income Recognized, Total	$ 1	$ 2	$ 5	$ 7