Loans and Allowance for Credit Losses for Loans - Summary of Allocation of Allowance for Loan Losses and Related Loans by Loan Portfolio Segment Disaggregated Based on Allowance Measurement Methodology (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	$ 60,432	$ 38,576
Collectively evaluated for impairment	222,910	123,183
Total	283,342	161,759	$ 154,381	$ 151,859
Individually evaluated for impairment	224,128	163,644
Collectively evaluated for impairment	30,203,939	22,905,965
Total	30,428,067	29,699,208
Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Loss [Line Items]
Total		6,629,599
Commercial and Industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	58,209	36,662
Collectively evaluated for impairment	69,228	67,397
Total	127,437	104,059	94,630	90,956
Individually evaluated for impairment	127,776	100,860
Collectively evaluated for impairment	4,870,955	4,043,123
Total	4,998,731	4,825,997
Commercial and Industrial | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Loss [Line Items]
Total		682,014
Commercial Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	1,383	1,338
Collectively evaluated for impairment	110,202	44,335
Total	111,585	45,673	47,762	49,650
Individually evaluated for impairment	76,239	51,242
Collectively evaluated for impairment	18,041,043	12,347,368
Total	18,117,282	17,643,759
Commercial Real Estate | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Loss [Line Items]
Total		5,245,149
Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	427	518
Collectively evaluated for impairment	29,029	4,542
Total	29,456	5,060	5,139	5,041
Individually evaluated for impairment	16,798	10,689
Collectively evaluated for impairment	4,462,184	3,786,253
Total	4,478,982	4,377,111
Residential Mortgage | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Loss [Line Items]
Total		580,169
Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	413	58
Collectively evaluated for impairment	14,451	6,909
Total	14,864	6,967	$ 6,850	$ 6,212
Individually evaluated for impairment	3,315	853
Collectively evaluated for impairment	2,829,757	2,729,221
Total	$ 2,833,072	2,852,341
Consumer | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Loss [Line Items]
Total		$ 122,267