Accumulated Other Comprehensive Loss (Summary of Activity in Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	$ 634,477	$ 593,538	$ 542,591
Balance	687,334	634,477	593,538
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(25,166)	(16,446)	(11,973)
Unrealized gain (loss)	5,858	(8,720)	(4,473)
Balance	(19,308)	(25,166)	(16,446)
Accumulated Net Loss from Cash Flow Hedges Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(40)	(114)	(111)
Unrealized gain (loss)	100	(72)	(317)
Reclassified to interest expense	116	244	523
Income tax expense	(46)	(98)	(209)
Balance	130	(40)	(114)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance	(25,206)	(16,560)	(12,084)
Balance	$ (19,178)	$ (25,206)	$ (16,560)