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, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for credit losses	$ 70,566		$ 75,871
Collectively evaluated for credit losses	268,758		264,372
Total	339,324	$ 342,880	340,243	$ 309,614	$ 283,342	$ 161,759
Individually evaluated for credit losses	253,171		229,593
Collectively evaluated for credit losses	32,204,283		31,987,519
Total	32,457,454		32,217,112
Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for credit losses	64,275		73,063
Collectively evaluated for credit losses	45,414		58,007
Total	109,689	126,408	131,070	132,039	127,437	104,059
Individually evaluated for credit losses	120,559		131,057
Collectively evaluated for credit losses	5,963,896		6,730,651
Total	6,084,455		6,861,708
Commercial Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for credit losses	4,788		1,338
Collectively evaluated for credit losses	184,351		162,775
Total	189,139	174,236	164,113	131,702	111,585	45,673
Individually evaluated for credit losses	89,464		61,754
Collectively evaluated for credit losses	19,175,516		18,409,069
Total	19,264,980		18,470,823
Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for credit losses	618		1,206
Collectively evaluated for credit losses	24,685		27,667
Total	25,303	27,172	28,873	29,630	29,456	5,060
Individually evaluated for credit losses	38,660		35,151
Collectively evaluated for credit losses	4,188,315		4,148,592
Total	4,226,975		4,183,743
Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for credit losses	885		264
Collectively evaluated for credit losses	14,308		15,923
Total	15,193	$ 15,064	16,187	$ 16,243	$ 14,864	$ 6,967
Individually evaluated for credit losses	4,488		1,631
Collectively evaluated for credit losses	2,876,556		2,699,207
Total	$ 2,881,044		$ 2,700,838