Fair-Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Interest expense	$ 18,602	$ 15,541	$ 11,841
Interest Rate Swap [Member]
Derivative [Line Items]
Interest expense	800	1,900	$ 1,900
Interest Rate Swap Buyouts [Member]
Derivative [Line Items]
Interest expense	700	$ 600
Interest Rate Swap Buyouts [Member] | Scenario, Forecast [Member]
Derivative [Line Items]
Interest income	$ 600