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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	$ 35,597		$ 35,597		$ 45,032
Without a related allowance, Unpaid Principal Balance	41,565		41,565		50,286
Without a related allowance recorded, Related Allowance	0		0		0
With a related allowance recorded, Recorded Investment	2,462		2,462		618
With a related allowance recorded, Unpaid Principal Balance	2,462		2,462		1,468
Impaired Financing Receivable, Recorded Investment	38,059		38,059		45,650
Impaired Financing Receivable, Unpaid Principal Balance, Total	44,027		44,027		51,754
Impaired Financing Receivable, Related Allowance	2,235		2,235		37
Without a related allowance recorded, Average Recorded Investment	34,665	$ 41,140	35,365	$ 40,631
Without a related allowance recorded, Interest Income Recognized	298	555	806	1,342
With a related allowance recorded, Average Recorded Investment	2,467	2,098	2,523	2,103
With a related allowance recorded, Interest Income Recognized	37	9	102	47
Impaired Financing Receivable, Average Recorded Investment, Total	37,132	43,238	37,888	42,734
Impaired Financing Receivable, Interest Income Recognized, Total	335	564	908	1,389
Commercial and Industrial
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	8,261		8,261		14,417
Without a related allowance, Unpaid Principal Balance	9,730		9,730		15,220
Without a related allowance recorded, Related Allowance	0		0		0
With a related allowance recorded, Recorded Investment	2,433		2,433		0
With a related allowance recorded, Unpaid Principal Balance	2,433		2,433		0
Impaired Financing Receivable, Recorded Investment	10,694		10,694		14,417
Impaired Financing Receivable, Unpaid Principal Balance, Total	12,163		12,163		15,220
Impaired Financing Receivable, Related Allowance	2,206		2,206		0
Without a related allowance recorded, Average Recorded Investment	7,326	8,993	7,447	9,742
Without a related allowance recorded, Interest Income Recognized	52	44	156	131
With a related allowance recorded, Average Recorded Investment	2,437	1,977	2,492	1,980
With a related allowance recorded, Interest Income Recognized	37	7	100	42
Impaired Financing Receivable, Average Recorded Investment, Total	9,763	10,970	9,939	11,722
Impaired Financing Receivable, Interest Income Recognized, Total	89	51	256	173
Commercial Real Estate
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	7,589		7,589		12,661
Without a related allowance, Unpaid Principal Balance	7,818		7,818		13,157
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
Impaired Financing Receivable, Recorded Investment	7,589		7,589		12,661
Impaired Financing Receivable, Unpaid Principal Balance, Total	7,818		7,818		13,157
Impaired Financing Receivable, Related Allowance	0		0		0
Without a related allowance recorded, Average Recorded Investment	7,582	14,101	7,551	14,994
Without a related allowance recorded, Interest Income Recognized	38	352	106	731
With a related allowance recorded, Average Recorded Investment	0	0	0	0
With a related allowance recorded, Interest Income Recognized	0	0	0	0
Impaired Financing Receivable, Average Recorded Investment, Total	7,582	14,101	7,551	14,994
Impaired Financing Receivable, Interest Income Recognized, Total	38	352	106	731
Commercial Construction
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	7,987		7,987		10,998
Without a related allowance, Unpaid Principal Balance	11,547		11,547		14,200
Without a related allowance recorded, Related Allowance	0		0		0
With a related allowance recorded, Recorded Investment	0		0		500
With a related allowance recorded, Unpaid Principal Balance	0		0		1,350
Impaired Financing Receivable, Recorded Investment	7,987		7,987		11,498
Impaired Financing Receivable, Unpaid Principal Balance, Total	11,547		11,547		15,550
Impaired Financing Receivable, Related Allowance	0		0		3
Without a related allowance recorded, Average Recorded Investment	8,039	11,034	8,498	8,920
Without a related allowance recorded, Interest Income Recognized	49	67	143	200
With a related allowance recorded, Average Recorded Investment	0	0		0
With a related allowance recorded, Interest Income Recognized	0	0		0
Impaired Financing Receivable, Average Recorded Investment, Total	8,039	11,034	8,498	8,920
Impaired Financing Receivable, Interest Income Recognized, Total	49	67	143	200
Consumer Real Estate
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	11,731		11,731		6,845
Without a related allowance, Unpaid Principal Balance	12,434		12,434		7,521
Without a related allowance recorded, Related Allowance	0		0		0
With a related allowance recorded, Recorded Investment	27		27		116
With a related allowance recorded, Unpaid Principal Balance	27		27		116
Impaired Financing Receivable, Recorded Investment	11,758		11,758		6,961
Impaired Financing Receivable, Unpaid Principal Balance, Total	12,461		12,461		7,637
Impaired Financing Receivable, Related Allowance	27		27		32
Without a related allowance recorded, Average Recorded Investment	11,686	6,829	11,831	6,856
Without a related allowance recorded, Interest Income Recognized	159	92	400	279
With a related allowance recorded, Average Recorded Investment	28	119	29	121
With a related allowance recorded, Interest Income Recognized	0	2	2	5
Impaired Financing Receivable, Average Recorded Investment, Total	11,714	6,948	11,860	6,977
Impaired Financing Receivable, Interest Income Recognized, Total	159	94	402	284
Other Consumer
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	29		29		111
Without a related allowance, Unpaid Principal Balance	36		36		188
Without a related allowance recorded, Related Allowance	0		0		0
With a related allowance recorded, Recorded Investment	2		2		2
With a related allowance recorded, Unpaid Principal Balance	2		2		2
Impaired Financing Receivable, Recorded Investment	31		31		113
Impaired Financing Receivable, Unpaid Principal Balance, Total	38		38		190
Impaired Financing Receivable, Related Allowance	2		2		$ 2
Without a related allowance recorded, Average Recorded Investment	32	183	38	119
Without a related allowance recorded, Interest Income Recognized	0	0	1	1
With a related allowance recorded, Average Recorded Investment	2	2	2	2
With a related allowance recorded, Interest Income Recognized	0	0	0	0
Impaired Financing Receivable, Average Recorded Investment, Total	34	185	40	121
Impaired Financing Receivable, Interest Income Recognized, Total	$ 0	$ 0	$ 1	$ 1