Allowance for Loan Losses - Age Analysis of Past Due Loans Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	$ 5,002,925	$ 3,850,597
Loans, Past Due	60,008	21,119
Loans, Non-performing	35,382	12,457
Total Loans	5,062,933	3,871,716
Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	2,145,655	1,674,930
Loans, Past Due	20,948	7,306
Loans, Non-performing	8,719	4,435
Total Loans	2,166,603	1,682,236
Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	1,244,802	991,136
Loans, Past Due	12,028	3,002
Loans, Non-performing	9,279	1,622
Total Loans	1,256,830	994,138
Commercial Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	401,084	214,174
Loans, Past Due	12,360	1,974
Loans, Non-performing	8,753	1,974
Total Loans	413,444	216,148
Residential Mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	631,085	485,465
Loans, Past Due	8,287	4,121
Loans, Non-performing	5,629	2,336
Total Loans	639,372	489,586
Home Equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	465,055	414,303
Loans, Past Due	5,790	4,260
Loans, Non-performing	2,902	2,059
Total Loans	470,845	418,563
Installment and Other Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	73,486	65,111
Loans, Past Due	453	456
Loans, Non-performing	100	31
Total Loans	73,939	65,567
Consumer Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	6,579	2,508
Loans, Past Due	0	0
Loans, Non-performing	0	0
Total Loans	6,579	2,508
Loans Held for Sale
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Current	35,179	2,970
Loans, Past Due	142	0
Loans, Non-performing	0	0
Total Loans	35,321	2,970
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	22,001	6,448
30-59 Days Past Due | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	11,602	2,548
30-59 Days Past Due | Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	2,453	1,227
30-59 Days Past Due | Commercial Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	3,517	0
30-59 Days Past Due | Residential Mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	1,728	565
30-59 Days Past Due | Home Equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	2,365	1,756
30-59 Days Past Due | Installment and Other Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	242	352
30-59 Days Past Due | Consumer Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	0	0
30-59 Days Past Due | Loans Held for Sale
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	94	0
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	2,625	2,214
60-89 Days Past Due | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	627	323
60-89 Days Past Due | Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	296	153
60-89 Days Past Due | Commercial Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	90	0
60-89 Days Past Due | Residential Mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	930	1,220
60-89 Days Past Due | Home Equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	523	445
60-89 Days Past Due | Installment and Other Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	111	73
60-89 Days Past Due | Consumer Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	0	0
60-89 Days Past Due | Loans Held for Sale
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Past Due	$ 48	$ 0