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	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for credit losses	$ 71,817		$ 75,871
Collectively evaluated for credit losses	270,710		264,372
Total	342,527	$ 339,324	340,243	$ 325,032	$ 309,614	$ 161,759
Individually evaluated for credit losses	306,542		229,593
Collectively evaluated for credit losses	32,300,272		31,987,519
Total	32,606,814		32,217,112
Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for credit losses	62,661		73,063
Collectively evaluated for credit losses	41,216		58,007
Total	103,877	109,689	131,070	130,409	132,039	104,059
Individually evaluated for credit losses	117,656		131,057
Collectively evaluated for credit losses	5,517,604		6,730,651
Total	5,635,260		6,861,708
Commercial Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for credit losses	8,093		1,338
Collectively evaluated for credit losses	191,628		162,775
Total	199,721	189,139	164,113	144,650	131,702	45,673
Individually evaluated for credit losses	143,181		61,754
Collectively evaluated for credit losses	19,573,469		18,409,069
Total	19,716,650		18,470,823
Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for credit losses	489		1,206
Collectively evaluated for credit losses	24,243		27,667
Total	24,732	25,303	28,873	28,614	29,630	5,060
Individually evaluated for credit losses	42,441		35,151
Collectively evaluated for credit losses	4,289,981		4,148,592
Total	4,332,422		4,183,743
Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for credit losses	574		264
Collectively evaluated for credit losses	13,623		15,923
Total	14,197	$ 15,193	16,187	$ 21,359	$ 16,243	$ 6,967
Individually evaluated for credit losses	3,264		1,631
Collectively evaluated for credit losses	2,919,218		2,699,207
Total	$ 2,922,482		$ 2,700,838