Derivatives and Hedging - Cash Flow Hedges (Details) - USD ($)		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Total amounts presented in the unaudited condensed consolidated statements of income		$ 644,643,000	$ 771,245,000	$ 2,029,886,000	$ 2,359,500,000
Total amounts presented in the unaudited condensed consolidated statements of income		14,644,000	32,975,000	$ 57,756,000	104,901,000
Derivatives designated as hedging instrument | Fair value hedges | Interest rate swap
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedges, weighted average expected remaining term				2 years 8 months 15 days
Derivatives designated as hedging instrument | Cash flow hedges | Interest rate swap
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on discontinuation of interest rate cash flow hedge due to forecasted transaction probable of not occurring, net		0	0	$ 0	0
Cash flow hedges not terminated, net fair value		(3,000,000)		$ (3,000,000)
Cash flow hedges, weighted average expected remaining term				2 years 4 months 30 days
Cash flow hedge gain (loss) to be reclassified within twelve months				$ 173,100,000
Maximum length of time hedged in interest rate cash flow hedge				4 years 2 months 6 days
Interest and Fees on Loans
Derivative Instruments, Gain (Loss) [Line Items]
Total amounts presented in the unaudited condensed consolidated statements of income		644,643,000	771,245,000	$ 2,029,886,000	2,359,500,000
Interest and Fees on Loans | Derivatives designated as hedging instrument | Fair value hedges
Gains (losses) on fair value hedging relationships:
Net income (expense) recognized on fair value hedges		0	0	0	0
Interest and Fees on Loans | Derivatives designated as hedging instrument | Fair value hedges | Interest rate contracts
Gains (losses) on fair value hedging relationships:
Amounts related to interest settlements and amortization on derivatives		0	0	0	0
Recognized on derivatives		0	0	0	0
Recognized on hedged items		0	0	0	0
Interest and Fees on Loans | Derivatives designated as hedging instrument | Cash flow hedges
Gain (losses) on cash flow hedging relationships:
Net income (expense) recognized on cash flow hedges	[1]	43,671,000	(295,000)	82,963,000	(2,765,000)
Interest and Fees on Loans | Derivatives designated as hedging instrument | Cash flow hedges | Interest rate contracts
Gain (losses) on cash flow hedging relationships:
Realized losses reclassified from AOCI into net income	[1],[2]	43,671,000	(295,000)	82,963,000	(2,765,000)
Interest on FHLB and other borrowings
Derivative Instruments, Gain (Loss) [Line Items]
Total amounts presented in the unaudited condensed consolidated statements of income		14,644,000	32,975,000	57,756,000	104,901,000
Interest on FHLB and other borrowings | Derivatives designated as hedging instrument | Fair value hedges
Gains (losses) on fair value hedging relationships:
Net income (expense) recognized on fair value hedges		11,898,000	234,000	26,929,000	(387,000)
Interest on FHLB and other borrowings | Derivatives designated as hedging instrument | Fair value hedges | Interest rate contracts
Gains (losses) on fair value hedging relationships:
Amounts related to interest settlements and amortization on derivatives		12,247,000	(136,000)	21,906,000	(4,192,000)
Recognized on derivatives		(12,407,000)	9,369,000	100,598,000	76,315,000
Recognized on hedged items		12,058,000	(8,999,000)	(95,575,000)	(72,510,000)
Interest on FHLB and other borrowings | Derivatives designated as hedging instrument | Cash flow hedges
Gain (losses) on cash flow hedging relationships:
Net income (expense) recognized on cash flow hedges	[1]	(832,000)	(254,000)	(1,841,000)	(584,000)
Interest on FHLB and other borrowings | Derivatives designated as hedging instrument | Cash flow hedges | Interest rate contracts
Gain (losses) on cash flow hedging relationships:
Realized losses reclassified from AOCI into net income	[1],[2]	$ (832,000)	$ (254,000)	$ (1,841,000)	$ (584,000)

[1] See Note 10, Comprehensive Income, for gain or loss recognized for cash flow hedges in accumulated other comprehensive income.

[2] Pre-tax