Financial Derivatives - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Derivative [Line Items]
Gain expected to be reclassified from AOCI to earnings over next 12 months	$ 5,200,000
Gain (loss) from interest rate swaps designated as cash flow hedges reclassified to earnings	0	$ 0
Investments held as collateral	0		$ 0
Cash posted as collateral			212,263,000
Financial derivatives in net payable position	0		0
Notional amount	15,711,679,000		15,447,553,000
Exchange Cleared
Derivative [Line Items]
Notional amount	13,500,000,000		12,800,000,000
Interest Rate Swap
Derivative [Line Items]
Notional amount	15,700,000,000		15,400,000,000
Cash
Derivative [Line Items]
Cash held as collateral	(4,900,000)		(1,300,000)
Cash posted as collateral	8,200,000		11,200,000
Available-for-Sale Securities
Derivative [Line Items]
Cash posted as collateral	$ 190,000,000.0		$ 201,100,000