Fair-Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Interest expense		$ 15,541	$ 11,841	$ 12,254
Interest Rate Swap [Member]
Derivative [Line Items]
Interest expense		1,700	$ 2,000	$ 1,900
Interest Rate Swap Buyouts [Member]
Derivative [Line Items]
Interest expense		$ 600
Interest Rate Swap Buyouts [Member] | Scenario, Forecast [Member]
Derivative [Line Items]
Interest expense	$ 500