Derivative Instruments Derivative Instruments (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Derivative, Notional Amount	$ 4,578,638	$ 4,525,856
Interest Rate Floor [Member]
Derivative [Line Items]
Derivative, Notional Amount	1,500,000	1,500,000
Premium paid for interest rate floor cash flow hedge	$ 31,300
Maximum Length of Time Hedged in Interest Rate Cash Flow Hedge	6 years 8 months 12 days
Unrealized gain (loss) on interest rate cash flow hedges, net of tax, amount recorded in accumulated other comprehensive income	$ 125,300
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	$ (4,100)
Interest Rate Floor [Member] | Interest Rate Floor 1 [Member]
Derivative [Line Items]
Derivative, Floor Interest Rate	2.25%
Derivative, Effective Date	Jan. 01, 2020
Derivative, Maturity Date	Jan. 01, 2026
Interest Rate Floor [Member] | Interest Rate Floor 2 [Member]
Derivative [Line Items]
Derivative, Floor Interest Rate	2.50%
Derivative, Effective Date	Jun. 01, 2020
Derivative, Maturity Date	Jun. 01, 2026
Interest Rate Floor [Member] | Interest Rate Floor 3 [Member]
Derivative [Line Items]
Derivative, Floor Interest Rate	2.00%
Derivative, Effective Date	Dec. 15, 2020
Derivative, Maturity Date	Dec. 15, 2026
Interest Rate Swaps [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 2,609,049	2,606,181
Variation Margin Impact to Positive Fair Values of Cleared Swaps	0	(617)
Variation Margin Impact to Negative Fair Values of Cleared Swaps	$ (79,400)	$ (28,500)