Derivatives - Effect of Derivative Instruments on Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Effect of derivative instruments on results of operations
Pre-tax gain recognized in other comprehensive income (loss)	$ 1,642	$ 1,919	$ 8,583	$ 2,282
Interest expense
Effect of derivative instruments on results of operations
Pre-tax gain (loss) reclassified from accumulated other comprehensive income (loss) into interest expense	$ 429	$ (678)	$ (83)	$ (2,521)