Loans and the Allowance for Credit Losses - Allowance for Credit Losses and Recorded Investments in Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	$ 6,728	$ 124
Allowance for loans collectively evaluated for impairment	107,544	52,305
Allowance for loan commitments	5,572	874	$ 1,960	$ 741
Total allowance for credit losses - loans and commitments	119,844	53,303	50,826	49,689
Individually evaluated for credit loss	24,066	21,017
Collectively-evaluated for credit losses	10,325,530	10,232,455
Acquired with deteriorated credit quality		14,513
Total loans	10,349,596	10,267,985
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	2,084	10
Allowance for loans collectively evaluated for impairment	37,143	14,106
Allowance for loan commitments		311	1,443	262
Total allowance for credit losses - loans and commitments	39,227	14,427	14,350	12,376
Individually evaluated for credit loss	4,527	11,961
Collectively-evaluated for credit losses	1,797,224	1,631,855
Acquired with deteriorated credit quality		883
Total loans	1,801,751	1,644,699
Deposit Overdrafts [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans collectively evaluated for impairment	1,064	1,387
Total allowance for credit losses - loans and commitments	1,064	1,387	1,205	972
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	5,604,405	5,725,008
Commercial Real Estate [Member] \| Commercial Real Estate - Land and Construction [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	692
Allowance for loans collectively evaluated for impairment	5,750	4,949
Allowance for loan commitments	5,111	235	194	169
Total allowance for credit losses - loans and commitments	11,553	5,184	4,239	4,208
Individually evaluated for credit loss	1,541
Collectively-evaluated for credit losses	675,185	777,033
Acquired with deteriorated credit quality		118
Total loans	676,726	777,151
Commercial Real Estate [Member] \| Commercial Real Estate - Improved Property [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment	3,952	93
Allowance for loans collectively evaluated for impairment	48,921	20,200
Allowance for loan commitments		22	24	33
Total allowance for credit losses - loans and commitments	52,873	20,315	19,939	20,881
Individually evaluated for credit loss	17,998	3,907
Collectively-evaluated for credit losses	4,909,681	4,935,383
Acquired with deteriorated credit quality		8,567
Total loans	4,927,679	4,947,857
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment		14
Allowance for loans collectively evaluated for impairment	9,684	4,297
Allowance for loan commitments	444	15	11	12
Total allowance for credit losses - loans and commitments	10,128	4,326	3,756	3,834
Individually evaluated for credit loss		4,392
Collectively-evaluated for credit losses	1,929,590	1,865,151
Acquired with deteriorated credit quality		4,104
Total loans	1,929,590	1,873,647
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment		1
Allowance for loans collectively evaluated for impairment	3,886	2,950
Allowance for loan commitments		41	40	39
Total allowance for credit losses - loans and commitments	3,886	2,992	2,820	2,836
Individually evaluated for credit loss		53
Collectively-evaluated for credit losses	363,096	374,812
Acquired with deteriorated credit quality		88
Total loans	363,096	374,953
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for loans individually evaluated for impairment		6
Allowance for loans collectively evaluated for impairment	1,096	4,416
Allowance for loan commitments	17	250	248	226
Total allowance for credit losses - loans and commitments	1,113	4,672	$ 4,517	$ 4,582
Individually evaluated for credit loss		704
Collectively-evaluated for credit losses	650,754	648,221
Acquired with deteriorated credit quality		753
Total loans	$ 650,754	$ 649,678

The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and allowance for loan losses). This relates to loans not accounted for debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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