Debt - Interest Rate Swaps (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($) derivative_instrument outstanding_contract	Dec. 31, 2018 USD ($) outstanding_contract
Derivative [Line Items]
Number of contracts | outstanding_contract	45	142
Notional amount	$ 2,340,826	$ 3,027,375
Interest rate swaps
Derivative [Line Items]
Number of contracts | derivative_instrument	5,000,000
Notional amount	$ 1,400,000
Number of active contracts | derivative_instrument	3
Term of contract	30 days
Net negative fair value (liability)	$ 64,600
Forward starting interest rate swap
Derivative [Line Items]
Number of contracts | derivative_instrument	2
Notional amount	$ 700,000
Minimum | Interest rate swaps
Derivative [Line Items]
Fixed interest rate	1.53%
Maximum | Interest rate swaps
Derivative [Line Items]
Fixed interest rate	2.13%