Loans and the Allowance for Credit Losses - Allowance for Credit Losses and Recorded Investments in Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	$ 877	$ 1,521
Allowance for loans collectively evaluated for impairment	42,797	40,189
Allowance for loan commitments	571	613	$ 455	$ 602
Total allowance for credit losses	44,245	42,323	45,109	47,970
Individually evaluated for impairment	4,282	8,903
Collectively evaluated for impairment	6,232,295	5,047,650
Acquired with deteriorated credit quality	12,859	9,289
Total Loans	6,249,436	5,065,842
Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	4,348	4,390
Allowance for loan commitments	151	157	194	301
Total allowance for credit losses	4,499	4,547	5,848	6,357
Collectively evaluated for impairment	494,928	343,832
Acquired with deteriorated credit quality	1,611	916
Total Loans	496,539	344,748
Commercial Real Estate - Improved Property [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	470	668
Allowance for loans collectively evaluated for impairment	18,158	14,080
Allowance for loan commitments	17	26	10	62
Total allowance for credit losses	18,645	14,774	17,583	18,219
Individually evaluated for impairment	3,012	4,031
Collectively evaluated for impairment	2,364,067	1,899,738
Acquired with deteriorated credit quality	9,893	7,864
Total Loans	2,376,972	1,911,633
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	407	853
Allowance for loans collectively evaluated for impairment	8,005	9,149
Allowance for loan commitments	188	260	112	130
Total allowance for credit losses	8,600	10,262	9,175	10,055
Individually evaluated for impairment	1,270	4,872
Collectively evaluated for impairment	1,086,445	732,957
Acquired with deteriorated credit quality	403	49
Total Loans	1,088,118	737,878
Deposit Overdraft [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	760	342
Total allowance for credit losses	760	342	575	520
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	4,106	4,582
Allowance for loan commitments	9	7	9	5
Total allowance for credit losses	4,115	4,589	5,391	5,678
Collectively evaluated for impairment	1,382,447	1,247,639
Acquired with deteriorated credit quality	943	161
Total Loans	1,383,390	1,247,800
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	3,998	4,763
Allowance for loan commitments	44	46	40	19
Total allowance for credit losses	4,042	4,809	4,118	5,039
Collectively evaluated for impairment	396,049	406,622
Acquired with deteriorated credit quality	9	272
Total Loans	396,058	406,894
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	3,422	2,883
Allowance for loan commitments	162	117	90	85
Total allowance for credit losses	3,584	3,000	$ 2,419	$ 2,102
Collectively evaluated for impairment	508,359	416,862
Acquired with deteriorated credit quality		27
Total Loans	$ 508,359	$ 416,889