Allowance for Credit Losses - Summary of Allocation of Allowance for Loan Losses and Related Loans by Loan Portfolio Segment Disaggregated Based on Impairment Methodology (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	$ 38,576,000	$ 33,025,000
Collectively evaluated for impairment	123,183,000	118,834,000
Allowance for loan losses	161,759,000	151,859,000	$ 120,856,000
Individually evaluated for impairment	163,644,000	156,625,000
Collectively evaluated for impairment	22,905,965,000	20,688,758,000
Total loans	29,699,208,000	25,035,469,000
Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for loan losses	0	0
Total loans	6,629,599,000	4,190,086,000
Commercial and Industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	36,662,000	29,684,000
Collectively evaluated for impairment	67,397,000	61,272,000
Allowance for loan losses	104,059,000	90,956,000	57,232,000
Individually evaluated for impairment	100,860,000	97,852,000
Collectively evaluated for impairment	4,043,123,000	3,492,523,000
Total loans	4,825,997,000	4,331,032,000
Commercial and Industrial | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Loss [Line Items]
Total loans	682,014,000	740,657,000
Commercial Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	1,338,000	2,628,000
Collectively evaluated for impairment	44,335,000	47,022,000
Allowance for loan losses	45,673,000	49,650,000	54,954,000
Individually evaluated for impairment	51,242,000	43,598,000
Collectively evaluated for impairment	12,347,368,000	10,991,059,000
Total loans	17,643,759,000	13,895,407,000
Commercial Real Estate | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Loss [Line Items]
Total loans	5,245,149,000	2,860,750,000
Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	518,000	600,000
Collectively evaluated for impairment	4,542,000	4,441,000
Allowance for loan losses	5,060,000	5,041,000	3,605,000
Individually evaluated for impairment	10,689,000	13,904,000
Collectively evaluated for impairment	3,786,253,000	3,669,080,000
Total loans	4,377,111,000	4,111,400,000
Residential Mortgage | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Loss [Line Items]
Total loans	580,169,000	428,416,000
Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	58,000	113,000
Collectively evaluated for impairment	6,909,000	6,099,000
Allowance for loan losses	6,967,000	6,212,000	$ 5,065,000
Individually evaluated for impairment	853,000	1,271,000
Collectively evaluated for impairment	2,729,221,000	2,536,096,000
Total loans	2,852,341,000	2,697,630,000
Consumer | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Loss [Line Items]
Total loans	$ 122,267,000	$ 160,263,000