Financial Derivatives - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Gain expected to be reclassified from AOCI to earnings over next 12 months	$ 900,000
Gain (loss) from interest rate swaps designated as cash flow hedges reclassified to earnings	0	$ 0
Investments held as collateral	0	(1,100,000)
Cash posted as collateral	132,129,000	47,018,000
Financial derivatives in net payable position	0	0
Notional amount	14,022,179,000	9,955,745,000
Cash
Derivative [Line Items]
Cash held as collateral	(2,700,000)	(700,000)
Cash posted as collateral	500,000	0
Available-for-Sale Securities
Derivative [Line Items]
Cash posted as collateral	131,700,000	47,000,000.0
Exchange Cleared
Derivative [Line Items]
Notional amount	11,000,000,000.0	8,500,000,000
Interest Rate Swap
Derivative [Line Items]
Notional amount	$ 14,000,000,000.0	$ 9,900,000,000