Commitments and Contingencies - Summary of Commitments (Details) - USD ($)	9 Months Ended
	Sep. 30, 2020		Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Loan commitments to extend credit	$ 7,178,506,000		$ 8,183,158,000
Standby letters of credit	353,820,000		355,503,000
Commitments to contribute capital to small business investment companies and CRA-related loan pools	52,941,000		40,698,000
Commitments to contribute capital to low income housing project partnerships	0	[1]	88,515,000
Commitments to contribute capital to private equity funds	50,000		50,000
Total	7,585,317,000		$ 8,667,924,000
Increase of investment in low income housing project partnerships	$ 101,000,000

[1] During the first quarter of 2020, the Company increased the amount of its investment in low income housing project partnerships by $101 million representing the amount of related unfunded commitments, with an offset to a liability included in "Accrued interest payable and other liabilities" on the condensed consolidated balance sheets.