Derivative Instruments and Hedging Activities - Balance Sheet Disclosures (Details) - USD ($)	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020
Interest rate swaps
Derivative [Line Items]
Other Assets	$ 0		$ 0
Other Liabilities	65,212,000		150,487,000
Interest rate swaps
Derivative [Line Items]
Notional Amount		$ 300,000,000
Derivatives designated as hedging instruments:
Derivative [Line Items]
Notional Amount	1,100,000,000		1,100,000,000
Derivatives designated as hedging instruments: | Other Assets
Derivative [Line Items]
Other Assets	0		0
Derivatives designated as hedging instruments: | Other Liabilities
Derivative [Line Items]
Other Liabilities	589,000		179,000
Derivatives designated as hedging instruments: | Cash flow hedge interest rate swaps | Interest rate swaps
Derivative [Line Items]
Notional Amount	800,000,000		1,100,000,000
Derivatives designated as hedging instruments: | Cash flow hedge interest rate swaps | Interest rate swaps | Other Assets
Derivative [Line Items]
Other Assets	0		0
Derivatives designated as hedging instruments: | Cash flow hedge interest rate swaps | Interest rate swaps | Other Liabilities
Derivative [Line Items]
Other Liabilities	273,000		179,000
Derivatives designated as hedging instruments: | Fair value hedge | Interest rate swaps
Derivative [Line Items]
Notional Amount	300,000,000		0
Derivatives designated as hedging instruments: | Fair value hedge | Interest rate swaps | Other Assets
Derivative [Line Items]
Other Assets	0		0
Derivatives designated as hedging instruments: | Fair value hedge | Interest rate swaps | Other Liabilities
Derivative [Line Items]
Other Liabilities	316,000		0
Derivatives not designated as hedging instruments:
Derivative [Line Items]
Notional Amount	10,623,584,000		9,211,043,000
Derivatives not designated as hedging instruments: | Other Assets
Derivative [Line Items]
Other Assets	215,919,000		387,452,000
Derivatives not designated as hedging instruments: | Other Liabilities
Derivative [Line Items]
Other Liabilities	66,144,000		156,102,000
Derivatives not designated as hedging instruments: | Interest rate swaps
Derivative [Line Items]
Notional Amount	10,296,468,000		8,889,557,000
Derivatives not designated as hedging instruments: | Interest rate swaps | Other Assets
Derivative [Line Items]
Other Assets	215,046,000		387,008,000
Derivatives not designated as hedging instruments: | Interest rate swaps | Other Liabilities
Derivative [Line Items]
Other Liabilities	64,623,000		154,025,000
Derivatives not designated as hedging instruments: | Mortgage banking derivatives
Derivative [Line Items]
Notional Amount	327,116,000		321,486,000
Derivatives not designated as hedging instruments: | Mortgage banking derivatives | Other Assets
Derivative [Line Items]
Other Assets	873,000		444,000
Derivatives not designated as hedging instruments: | Mortgage banking derivatives | Other Liabilities
Derivative [Line Items]
Other Liabilities	1,521,000		$ 2,077,000
Derivatives not designated as hedging instruments: | Fair value hedge | Interest rate swaps
Derivative [Line Items]
Notional Amount	$ 10,400,000