Derivative Instruments and Hedging Activities - Balance Sheet Disclosures (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Interest rate swaps
Derivative [Line Items]
Other Assets	$ 0	$ 0
Other Liabilities	187,033,000	43,733,000
Derivatives designated as hedging instruments
Derivative [Line Items]
Other Assets	0	0
Other Liabilities	4,292,000	1,713,000
Notional Amount	1,182,079,000	187,281,000
Derivatives designated as hedging instruments | Cash flow hedge interest rate swaps
Derivative [Line Items]
Notional Amount	1,100,000,000
Derivatives designated as hedging instruments | Cash flow hedge interest rate swaps | Interest rate swaps
Derivative [Line Items]
Other Assets	0	0
Other Liabilities	4,233,000	1,484,000
Notional Amount	1,175,000,000	180,000,000
Derivatives designated as hedging instruments | Fair value hedge interest rate swaps | Interest rate swaps
Derivative [Line Items]
Other Assets	0	0
Other Liabilities	59,000	229,000
Notional Amount	7,079,000	7,281,000
Derivatives not designated as hedging instruments
Derivative [Line Items]
Other Assets	455,565,000	158,532,000
Other Liabilities	185,757,000	42,213,000
Notional Amount	8,827,975,000	4,255,866,000
Derivatives not designated as hedging instruments | Interest rate swaps
Derivative [Line Items]
Other Assets	455,404,000	158,382,000
Other Liabilities	182,741,000	42,020,000
Notional Amount	8,306,557,000	4,113,106,000
Derivatives not designated as hedging instruments | Mortgage banking derivatives
Derivative [Line Items]
Other Assets	161,000	150,000
Other Liabilities	3,016,000	193,000
Notional Amount	$ 521,418,000	$ 142,760,000