Allowance for Loan Losses - Investments in Loans Considered to be Impaired and Related Information on Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	$ 44,982		$ 44,982		$ 43,914
Without a related allowance, Unpaid Principal Balance	58,282		58,282		53,785
Without a related allowance recorded, Related Allowance	0		0		0
With a related allowance recorded, Recorded Investment	873		873		63
With a related allowance recorded, Unpaid Principal Balance	873		873		63
Impaired Financing Receivable, Recorded Investment, Total	45,855		45,855		43,977
Impaired Financing Receivable, Unpaid Principal Balance, Total	59,155		59,155		53,848
Impaired Financing Receivable, Related Allowance	608		608		54
Without a related allowance recorded, Average Recorded Investment	45,651	$ 46,253	45,274	$ 46,719
Without a related allowance recorded, Interest Income Recognized	418	374	792	762
With a related allowance recorded, Average Recorded Investment	545	70	337	73
With a related allowance recorded, Interest Income Recognized	2	1	3	3
Impaired Financing Receivable, Average Recorded Investment, Total	46,196	46,323	45,611	46,792
Impaired Financing Receivable, Interest Income Recognized, Total	420	375	795	765
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	18,548		18,548		19,890
Without a related allowance, Unpaid Principal Balance	25,698		25,698		25,262
With a related allowance recorded, Recorded Investment	749		749
With a related allowance recorded, Unpaid Principal Balance	749		749
Impaired Financing Receivable, Recorded Investment, Total	19,297		19,297		19,890
Impaired Financing Receivable, Unpaid Principal Balance, Total	26,447		26,447		25,262
Impaired Financing Receivable, Related Allowance	567		567
Without a related allowance recorded, Average Recorded Investment	19,733	21,382	20,455	21,980
Without a related allowance recorded, Interest Income Recognized	158	159	322	329
With a related allowance recorded, Average Recorded Investment	420		211
Impaired Financing Receivable, Average Recorded Investment, Total	20,153	21,382	20,666	21,980
Impaired Financing Receivable, Interest Income Recognized, Total	158	159	322	329
Commercial and Industrial [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	10,125		10,125		9,218
Without a related allowance, Unpaid Principal Balance	11,877		11,877		9,449
Impaired Financing Receivable, Recorded Investment, Total	10,125		10,125		9,218
Impaired Financing Receivable, Unpaid Principal Balance, Total	11,877		11,877		9,449
Without a related allowance recorded, Average Recorded Investment	10,782	9,317	11,162	9,066
Without a related allowance recorded, Interest Income Recognized	84	57	146	114
Impaired Financing Receivable, Average Recorded Investment, Total	10,782	9,317	11,162	9,066
Impaired Financing Receivable, Interest Income Recognized, Total	84	57	146	114
Construction Loans [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	9,293		9,293		7,605
Without a related allowance, Unpaid Principal Balance	12,983		12,983		11,293
Impaired Financing Receivable, Recorded Investment, Total	9,293		9,293		7,605
Impaired Financing Receivable, Unpaid Principal Balance, Total	12,983		12,983		11,293
Without a related allowance recorded, Average Recorded Investment	8,119	8,279	6,628	8,301
Without a related allowance recorded, Interest Income Recognized	81	57	134	114
Impaired Financing Receivable, Average Recorded Investment, Total	8,119	8,279	6,628	8,301
Impaired Financing Receivable, Interest Income Recognized, Total	81	57	134	114
Consumer Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	6,824		6,824		7,159
Without a related allowance, Unpaid Principal Balance	7,527		7,527		7,733
With a related allowance recorded, Recorded Investment	120		120		43
With a related allowance recorded, Unpaid Principal Balance	120		120		43
Impaired Financing Receivable, Recorded Investment, Total	6,944		6,944		7,202
Impaired Financing Receivable, Unpaid Principal Balance, Total	7,647		7,647		7,776
Impaired Financing Receivable, Related Allowance	37		37		43
Without a related allowance recorded, Average Recorded Investment	6,891	7,166	6,943	7,260
Without a related allowance recorded, Interest Income Recognized	91	100	186	203
With a related allowance recorded, Average Recorded Investment	121	48	122	50
With a related allowance recorded, Interest Income Recognized	2	1	3	2
Impaired Financing Receivable, Average Recorded Investment, Total	7,012	7,214	7,065	7,310
Impaired Financing Receivable, Interest Income Recognized, Total	93	101	189	205
Other Consumer [Member]
Financing Receivable, Impaired [Line Items]
Without a related allowance recorded, Recorded Investment	192		192		42
Without a related allowance, Unpaid Principal Balance	197		197		48
With a related allowance recorded, Recorded Investment	4		4		20
With a related allowance recorded, Unpaid Principal Balance	4		4		20
Impaired Financing Receivable, Recorded Investment, Total	196		196		62
Impaired Financing Receivable, Unpaid Principal Balance, Total	201		201		68
Impaired Financing Receivable, Related Allowance	4		4		$ 11
Without a related allowance recorded, Average Recorded Investment	126	109	86	112
Without a related allowance recorded, Interest Income Recognized	4	1	4	2
With a related allowance recorded, Average Recorded Investment	4	22	4	23
With a related allowance recorded, Interest Income Recognized				1
Impaired Financing Receivable, Average Recorded Investment, Total	130	131	90	135
Impaired Financing Receivable, Interest Income Recognized, Total	$ 4	$ 1	$ 4	$ 3