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	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	$ 71,498		$ 38,576
Collectively evaluated for impairment	238,116		123,183
Total	309,614	$ 283,342	161,759	$ 155,105	$ 154,381	$ 151,859
Individually evaluated for impairment	241,278		163,644
Collectively evaluated for impairment	32,073,333		22,905,965
Total	32,314,611		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	69,333		36,662
Collectively evaluated for impairment	62,706		67,397
Total	132,039	127,437	104,059	94,384	94,630	90,956
Individually evaluated for impairment	138,120		100,860
Collectively evaluated for impairment	6,746,569		4,043,123
Total	6,884,689		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	1,237		1,338
Collectively evaluated for impairment	130,465		44,335
Total	131,702	111,585	45,673	48,978	47,762	49,650
Individually evaluated for impairment	77,914		51,242
Collectively evaluated for impairment	18,215,315		12,347,368
Total	18,293,229		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	430		518
Collectively evaluated for impairment	29,200		4,542
Total	29,630	29,456	5,060	5,219	5,139	5,041
Individually evaluated for impairment	22,148		10,689
Collectively evaluated for impairment	4,382,999		3,786,253
Total	4,405,147		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	498		58
Collectively evaluated for impairment	15,745		6,909
Total	16,243	$ 14,864	6,967	$ 6,524	$ 6,850	$ 6,212
Individually evaluated for impairment	3,096		853
Collectively evaluated for impairment	2,728,450		2,729,221
Total	$ 2,731,546		2,852,341
Consumer | Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Loss [Line Items]
Total			$ 122,267