Loans and the Allowance for Credit Losses - Summary of Age Analysis of Loan Categories (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Current	$ 10,195,872	$ 7,610,687
Total Past Due	72,113	45,594
Total loans	10,267,985	7,656,281
90 Days or More Past Due and Accruing	11,613	4,077
Loans held for sale, current	43,013	8,994
Loans held for sale	43,013	8,994
Total loans, current	10,238,885	7,619,681
Total loans	10,310,998	7,665,275
Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	641,026	591,623
Total Past Due	8,652	7,708
Total loans	649,678	599,331
90 Days or More Past Due and Accruing	985	705
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	5,697,874	3,841,425
Total Past Due	27,134	12,270
Total loans	5,725,008	3,853,695
90 Days or More Past Due and Accruing	4,735	175
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	1,850,806	1,593,519
Total Past Due	22,841	18,088
Total loans	1,873,647	1,611,607
90 Days or More Past Due and Accruing	3,643	2,820
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	370,934	322,584
Total Past Due	4,019	3,604
Total loans	374,953	326,188
90 Days or More Past Due and Accruing	457	364
Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	776,153	526,660
Total Past Due	998	1,412
Total loans	777,151	528,072
90 Days or More Past Due and Accruing	26
Commercial Real Estate - Improved Property [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	4,921,721	3,314,765
Total Past Due	26,136	10,858
Total loans	4,947,857	3,325,623
90 Days or More Past Due and Accruing	4,709	175
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	1,635,232	1,261,536
Total Past Due	9,467	3,924
Total loans	1,644,699	1,265,460
90 Days or More Past Due and Accruing	1,793	13
Non-Accrual Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	21,061	8,910
Total Past Due	23,852	21,790
Total loans	44,913	30,700
TDRs Accruing Interest [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	5,113	5,586
Total Past Due	318	158
Total loans	5,431	5,744
Total Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Current	26,174	14,496
Total Past Due	24,170	21,948
Total loans	50,344	36,444
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	23,536	9,952
30-59 Days Past Due [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	3,323	2,500
30-59 Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	10,736	2,328
30-59 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	4,421	2,717
30-59 Days Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	2,537	2,084
30-59 Days Past Due [Member] | Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	529	62
30-59 Days Past Due [Member] | Commercial Real Estate - Improved Property [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	10,207	2,266
30-59 Days Past Due [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	2,519	323
30-59 Days Past Due [Member] | Non-Accrual Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	897	337
30-59 Days Past Due [Member] | TDRs Accruing Interest [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	151	59
30-59 Days Past Due [Member] | Total Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	1,048	396
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	15,531	11,475
60-89 Days Past Due [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	621	1,273
60-89 Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	5,760	3,600
60-89 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	5,372	5,001
60-89 Days Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	965	1,007
60-89 Days Past Due [Member] | Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	121	1,350
60-89 Days Past Due [Member] | Commercial Real Estate - Improved Property [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	5,639	2,250
60-89 Days Past Due [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	2,813	594
60-89 Days Past Due [Member] | Non-Accrual Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	1,559	1,370
60-89 Days Past Due [Member] | TDRs Accruing Interest [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	130	92
60-89 Days Past Due [Member] | Total Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	1,689	1,462
90 Days or More Past Due [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	33,046	24,167
90 Days or More Past Due [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	4,708	3,935
90 Days or More Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	10,638	6,342
90 Days or More Past Due [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	13,048	10,370
90 Days or More Past Due [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	517	513
90 Days or More Past Due [Member] | Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	348
90 Days or More Past Due [Member] | Commercial Real Estate - Improved Property [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	10,290	6,342
90 Days or More Past Due [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	4,135	3,007
90 Days or More Past Due [Member] | Non-Accrual Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	21,396	20,083
90 Days or More Past Due [Member] | TDRs Accruing Interest [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	37	7
90 Days or More Past Due [Member] | Total Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Past Due	$ 21,433	$ 20,090