Derivative Instruments - Swap of Terms (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Mar. 31, 2020
Interest rate swaps and interest rate swaptions
Notional Amount	$ 1,000,000	$ 778,200
Derivative liability, at fair value	(6,370)	(43,967)
Derivative cash collateral	2,819	25,538
Derivative instruments not accounted as hedges under GAAP
Interest rate swaps and interest rate swaptions
Derivative liability, at fair value	(6,370)	(43,967)
Fair Value	(1,259)	(10,292)
Interest rate swaps | Derivative instruments not accounted as hedges under GAAP
Interest rate swaps and interest rate swaptions
Notional amount, assets	2,701,000	0
Notional amount, liabilities	1,255,000	0
Derivative liability, at fair value	(501)	0
Interest rate swaps | Derivative instruments not accounted as hedges under GAAP | Fixed Pay Rate
Interest rate swaps and interest rate swaptions
Notional Amount	$ 2,551,000
Derivative, average fixed interest rate	2.20%
Derivative, average variable interest rate	2.00%
Weighted Average Months Until Option Expiration	7 years 1 month 6 days
Interest rate swaps | Derivative instruments not accounted as hedges under GAAP | Variable Pay Rate
Interest rate swaps and interest rate swaptions
Notional Amount	$ 1,405,000
Derivative, average fixed interest rate	2.00%
Derivative, average variable interest rate	1.90%
Weighted Average Months Until Option Expiration	3 years 6 months
Interest rate swaps | Derivative instruments not accounted as hedges under GAAP | One Year Or Less | Fixed Pay Rate
Interest rate swaps and interest rate swaptions
Notional Amount	$ 200,000
Derivative, average fixed interest rate	1.80%
Derivative, average variable interest rate	1.90%
Weighted Average Months Until Option Expiration	4 months 24 days
Interest rate swaps | Derivative instruments not accounted as hedges under GAAP | Greater Than Three Years And Less Than Five Years | Fixed Pay Rate
Interest rate swaps and interest rate swaptions
Notional Amount	$ 622,400
Derivative, average fixed interest rate	2.60%
Derivative, average variable interest rate	1.90%
Weighted Average Months Until Option Expiration	4 years 1 month 6 days
Interest rate swaps | Derivative instruments not accounted as hedges under GAAP | Greater Than Three Years And Less Than Five Years | Variable Pay Rate
Interest rate swaps and interest rate swaptions
Notional Amount	$ 550,000
Derivative, average fixed interest rate	1.90%
Derivative, average variable interest rate	1.60%
Weighted Average Months Until Option Expiration	5 years
Interest rate swaps | Derivative instruments not accounted as hedges under GAAP | Greater Than Five Years | Fixed Pay Rate
Interest rate swaps and interest rate swaptions
Notional Amount	$ 1,728,600
Derivative, average fixed interest rate	2.10%
Derivative, average variable interest rate	2.00%
Weighted Average Months Until Option Expiration	8 years 10 months 24 days
Interest rate swaps | Derivative instruments not accounted as hedges under GAAP | Greater Than Five Years | Variable Pay Rate
Interest rate swaps and interest rate swaptions
Notional Amount	$ 45,000
Derivative, average fixed interest rate	190000.00%
Derivative, average variable interest rate	230000.00%
Weighted Average Months Until Option Expiration	19 years 6 months
Interest rate swaps | Derivative instruments not accounted as hedges under GAAP | Greater Than One Year And Less Than Three Years | Variable Pay Rate
Interest rate swaps and interest rate swaptions
Notional Amount	$ 810,000
Derivative, average fixed interest rate	2.00%
Derivative, average variable interest rate	2.00%
Weighted Average Months Until Option Expiration	1 year 7 months 6 days
Credit default swaps | Derivative instruments not accounted as hedges under GAAP
Interest rate swaps and interest rate swaptions
Notional amount, assets	$ 60,100	47,260
Notional amount, liabilities	90,900	97,260
Derivative liability, at fair value	$ (3,795)	$ (22,106)