Loans and the Allowance for Credit Losses - Summary of Age Analysis of Loan Categories (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Current	$ 6,204,822	$ 5,028,841
Total Past Due	44,614	37,001
Total Loans	6,249,436	5,065,842
90 Days or More Past Due and Accruing	3,739	3,126
Loans held for sale, current	17,315	7,899
Loans held for sale	17,315	7,899
Total loans, current	6,222,137	5,036,740
Total loans	6,266,751	5,073,741
Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	502,087	412,450
Total Past Due	6,272	4,439
Total Loans	508,359	416,889
90 Days or More Past Due and Accruing	626	407
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	2,864,035	2,245,650
Total Past Due	9,476	10,731
Total Loans	2,873,511	2,256,381
90 Days or More Past Due and Accruing	318
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	1,365,956	1,234,839
Total Past Due	17,434	12,961
Total Loans	1,383,390	1,247,800
90 Days or More Past Due and Accruing	1,922	2,159
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	390,354	401,242
Total Past Due	5,704	5,652
Total Loans	396,058	406,894
90 Days or More Past Due and Accruing	644	527
Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	496,245	344,184
Total Past Due	294	564
Total Loans	496,539	344,748
Commercial Real Estate - Improved Property [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	2,367,790	1,901,466
Total Past Due	9,182	10,167
Total Loans	2,376,972	1,911,633
90 Days or More Past Due and Accruing	318
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	1,082,390	734,660
Total Past Due	5,728	3,218
Total Loans	1,088,118	737,878
90 Days or More Past Due and Accruing	229	33
Non-Accrual Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	7,570	11,349
Total Past Due	24,214	22,032
Total Loans	31,784	33,381
TDRs Accruing Interest [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	7,014	10,710
Total Past Due	632	838
Total Loans	7,646	11,548
Total Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	14,584	22,059
Total Past Due	24,846	22,870
Total Loans	39,430	44,929
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	16,395	8,963
30-59 Days Past Due [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	2,358	2,252
30-59 Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	1,154	909
30-59 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	6,701	1,389
30-59 Days Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	3,674	4,115
30-59 Days Past Due [Member] | Commercial Real Estate - Improved Property [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	1,154	909
30-59 Days Past Due [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	2,508	298
30-59 Days Past Due [Member] | Non-Accrual Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	3,479	943
30-59 Days Past Due [Member] | TDRs Accruing Interest [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	342	390
30-59 Days Past Due [Member] | Total Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	3,821	1,333
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	4,428	5,760
60-89 Days Past Due [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	862	314
60-89 Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	363	1,097
60-89 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	1,043	2,871
60-89 Days Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	1,149	764
60-89 Days Past Due [Member] | Commercial Real Estate - Improved Property [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	363	1,097
60-89 Days Past Due [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	1,011	714
60-89 Days Past Due [Member] | Non-Accrual Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	923	2,147
60-89 Days Past Due [Member] | TDRs Accruing Interest [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	50	238
60-89 Days Past Due [Member] | Total Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	973	2,385
90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	23,791	22,278
90 Days or More Past Due [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	3,052	1,873
90 Days or More Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	7,959	8,725
90 Days or More Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	9,690	8,701
90 Days or More Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	881	773
90 Days or More Past Due [Member] | Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	294	564
90 Days or More Past Due [Member] | Commercial Real Estate - Improved Property [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	7,665	8,161
90 Days or More Past Due [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	2,209	2,206
90 Days or More Past Due [Member] | Non-Accrual Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	19,812	18,942
90 Days or More Past Due [Member] | TDRs Accruing Interest [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	240	210
90 Days or More Past Due [Member] | Total Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	$ 20,052	$ 19,152