Derivatives - Derivative Gain (Loss) Recognized in Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Effect of derivative instruments on results of operations
Total amounts of income and expense line items presented in the statement of operations in which the effects of cash flow hedges are recorded	$ 22,547	$ 21,421
Interest expense
Effect of derivative instruments on results of operations
Amount of loss reclassified from accumulated other comprehensive income into income	(474)	$ (1,013)
Derivatives designated as cash flow hedges | Interest rate swaps | Interest expense
Effect of derivative instruments on results of operations
Amount of loss reclassified from accumulated other comprehensive income into income	(54)
Amount of gain or (loss) reclassified from accumulated other comprehensive income into income as a result that a forecasted transaction is no longer probable of occurring	$ 0