Derivatives - Interest Rate Swaps (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Accumulated other comprehensive loss	$ (2,000,000)	$ (2,000,000)		$ (2,200,000)
Cash flow hedge gain (loss) amortized into interest rate expense	0	0
Cash flow hedge gain (loss) amortized into interest rate expense in the next 12 months	(100,000)
Derivatives
Realized gain (loss) on derivatives	5,200,000	$ (4,200,000)	$ (11,100,000)
Interest Rate Swap
Derivatives
Outstanding interest rate swaps	$ 0
Realized gain (loss) on derivatives			$ 400,000