Derivative Financial Instruments - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Total amount of notional derivative contracts	$ 6,000,000
Net positive exposure	27,000	$ 20,000
Estimated reclassification of AOCI to interest expense	5,500
Cash collateral pledged	27,200	21,600
CME
Derivative [Line Items]
Total amount of notional derivative contracts	$ 5,400,000
Percentage of total notional derivative contracts	90.20%
Amount of variation margin included as settlement	$ (16,700)
LCH
Derivative [Line Items]
Total amount of notional derivative contracts	$ 600,000
Percentage of total notional derivative contracts	9.80%
Amount of variation margin included as settlement	$ (6,100)
Interest Rate Swaps
Derivative [Line Items]
Total amount of notional derivative contracts	5,996,310	5,459,075
Fair Value | Interest Rate Swaps | Designated as Hedging Instrument
Derivative [Line Items]
Total amount of notional derivative contracts	$ 3,137,965	$ 3,062,849