Condensed Consolidating Statement Of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed Statement of Income Captions [Line Items]
Net income	$ 25,086	$ 24,269
Other comprehensive income, net of tax:
Amortization of loss on cash flow hedge	215	215
Foreign currency translation adjustment	855	568
Other comprehensive income, net of tax	1,070	783
Comprehensive income	26,156	25,052
Parent
Condensed Statement of Income Captions [Line Items]
Net income	25,086	24,269
Other comprehensive income, net of tax:
Amortization of loss on cash flow hedge	215	215
Foreign currency translation adjustment	855	568
Other comprehensive income, net of tax	1,070	783
Comprehensive income	26,156	25,052
Guarantor Subsidiaries
Condensed Statement of Income Captions [Line Items]
Net income	6,327	5,666
Other comprehensive income, net of tax:
Amortization of loss on cash flow hedge	0	0
Foreign currency translation adjustment	0	0
Other comprehensive income, net of tax	0	0
Comprehensive income	6,327	5,666
Non-Guarantor Subsidiaries
Condensed Statement of Income Captions [Line Items]
Net income	3,368	7,071
Other comprehensive income, net of tax:
Amortization of loss on cash flow hedge	0	0
Foreign currency translation adjustment	855	568
Other comprehensive income, net of tax	855	568
Comprehensive income	4,223	7,639
Eliminations
Condensed Statement of Income Captions [Line Items]
Net income	(9,695)	(12,737)
Other comprehensive income, net of tax:
Amortization of loss on cash flow hedge	0	0
Foreign currency translation adjustment	(855)	(568)
Other comprehensive income, net of tax	(855)	(568)
Comprehensive income	$ (10,550)	$ (13,305)