Derivative Instruments Derivative Instruments (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Apr. 01, 2019	Dec. 31, 2018
Derivative [Line Items]
Notional Amount of Derivatives	$ 3,277,127		$ 3,254,921
Interest Rate Floor [Member]
Derivative [Line Items]
Notional Amount of Derivatives	1,000,000		1,000,000
Premium paid for interest rate floor cash flow hedge	$ 20,700
Maximum Length of Time Hedged in Interest Rate Cash Flow Hedge	6 years 5 months
Unrealized gain (loss) on interest rate cash flow hedges, net of tax, amount recorded in accumulated other comprehensive income	$ 12,800
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	(2,800)
Interest Rate Swaps [Member]
Derivative [Line Items]
Notional Amount of Derivatives	2,007,799		2,006,280
Variation Margin Impact to Positive Fair Values of Cleared Swaps	(3,800)		(8,100)
Variation Margin Impact to Negative Fair Values of Cleared Swaps	$ (12,400)		$ (6,500)
Subsequent Event [Member] | Interest Rate Floor [Member]
Derivative [Line Items]
Notional Amount of Derivatives		$ 500,000
Premium paid for interest rate floor cash flow hedge		$ 10,700
Derivative, Floor Interest Rate		2.00%
Maximum [Member] | Interest Rate Floor [Member]
Derivative [Line Items]
Derivative, Floor Interest Rate	2.50%
Minimum [Member] | Interest Rate Floor [Member]
Derivative [Line Items]
Derivative, Floor Interest Rate	2.25%