Allowance for Loan Losses - Investments in Loans Considered to be Impaired and Related Information on Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	$ 39,112		$ 39,112		$ 43,914
Without a related allowance, Unpaid Principal Balance	46,063		46,063		53,785
Without a related allowance recorded, Related Allowance	0		0		0
With a related allowance recorded, Recorded Investment	2,089		2,089		63
With a related allowance recorded, Unpaid Principal Balance	2,089		2,089		63
Impaired Financing Receivable, Recorded Investment, Total	41,201		41,201		43,977
Impaired Financing Receivable, Unpaid Principal Balance, Total	48,152		48,152		53,848
Impaired Financing Receivable, Related Allowance	1,260		1,260		54
Without a related allowance recorded, Average Recorded Investment	41,140	$ 46,121	40,631	$ 46,627
Without a related allowance recorded, Interest Income Recognized	555	381	1,342	1,170
With a related allowance recorded, Average Recorded Investment	2,098	70	2,103	73
With a related allowance recorded, Interest Income Recognized	9	1	47	4
Impaired Financing Receivable, Average Recorded Investment, Total	43,238	46,191	42,734	46,700
Impaired Financing Receivable, Interest Income Recognized, Total	564	382	1,389	1,174
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	14,080		14,080		19,890
Without a related allowance, Unpaid Principal Balance	14,576		14,576		25,262
With a related allowance recorded, Recorded Investment	0		0
With a related allowance recorded, Unpaid Principal Balance	0		0
Impaired Financing Receivable, Recorded Investment, Total	14,080		14,080		19,890
Impaired Financing Receivable, Unpaid Principal Balance, Total	14,576		14,576		25,262
Impaired Financing Receivable, Related Allowance	0		0
Without a related allowance recorded, Average Recorded Investment	14,101	21,110	14,994	21,593
Without a related allowance recorded, Interest Income Recognized	352	159	731	512
With a related allowance recorded, Average Recorded Investment	0		0
Impaired Financing Receivable, Average Recorded Investment, Total	14,101	21,110	14,994	21,593
Impaired Financing Receivable, Interest Income Recognized, Total	352	159	731	512
Commercial Construction [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	9,315		9,315		7,605
Without a related allowance, Unpaid Principal Balance	12,977		12,977		11,293
Impaired Financing Receivable, Recorded Investment, Total	9,315		9,315		7,605
Impaired Financing Receivable, Unpaid Principal Balance, Total	12,977		12,977		11,293
Without a related allowance recorded, Average Recorded Investment	11,034	8,160	8,920	8,254
Without a related allowance recorded, Interest Income Recognized	67	58	200	172
Impaired Financing Receivable, Average Recorded Investment, Total	11,034	8,160	8,920	8,254
Impaired Financing Receivable, Interest Income Recognized, Total	67	58	200	172
Consumer Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	6,852		6,852		7,159
Without a related allowance, Unpaid Principal Balance	7,401		7,401		7,733
With a related allowance recorded, Recorded Investment	118		118		43
With a related allowance recorded, Unpaid Principal Balance	118		118		43
Impaired Financing Receivable, Recorded Investment, Total	6,970		6,970		7,202
Impaired Financing Receivable, Unpaid Principal Balance, Total	7,519		7,519		7,776
Impaired Financing Receivable, Related Allowance	34		34		43
Without a related allowance recorded, Average Recorded Investment	6,829	7,034	6,856	7,181
Without a related allowance recorded, Interest Income Recognized	92	100	279	306
With a related allowance recorded, Average Recorded Investment	119	47	121	49
With a related allowance recorded, Interest Income Recognized	2	1	5	2
Impaired Financing Receivable, Average Recorded Investment, Total	6,948	7,081	6,977	7,230
Impaired Financing Receivable, Interest Income Recognized, Total	94	101	284	308
Other Consumer [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	119		119		42
Without a related allowance, Unpaid Principal Balance	191		191		48
With a related allowance recorded, Recorded Investment	2		2		20
With a related allowance recorded, Unpaid Principal Balance	2		2		20
Impaired Financing Receivable, Recorded Investment, Total	121		121		62
Impaired Financing Receivable, Unpaid Principal Balance, Total	193		193		68
Impaired Financing Receivable, Related Allowance	2		2		11
Without a related allowance recorded, Average Recorded Investment	183	115	119	122
Without a related allowance recorded, Interest Income Recognized	0	1	1	3
With a related allowance recorded, Average Recorded Investment	2	23	2	24
With a related allowance recorded, Interest Income Recognized				2
Impaired Financing Receivable, Average Recorded Investment, Total	185	138	121	146
Impaired Financing Receivable, Interest Income Recognized, Total	0	1	1	5
Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	8,746		8,746		9,218
Without a related allowance, Unpaid Principal Balance	10,918		10,918		9,449
With a related allowance recorded, Recorded Investment	1,969		1,969
With a related allowance recorded, Unpaid Principal Balance	1,969		1,969
Impaired Financing Receivable, Recorded Investment, Total	10,715		10,715		9,218
Impaired Financing Receivable, Unpaid Principal Balance, Total	12,887		12,887		$ 9,449
Impaired Financing Receivable, Related Allowance	1,224		1,224
Without a related allowance recorded, Average Recorded Investment	8,993	9,702	9,742	9,477
Without a related allowance recorded, Interest Income Recognized	44	63	131	177
With a related allowance recorded, Average Recorded Investment	1,977		1,980
With a related allowance recorded, Interest Income Recognized	7		42
Impaired Financing Receivable, Average Recorded Investment, Total	10,970	9,702	11,722	9,477
Impaired Financing Receivable, Interest Income Recognized, Total	$ 51	$ 63	$ 173	$ 177