Condensed Consolidating Statement Of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014		Sep. 30, 2015	Sep. 30, 2014
Condensed Statement of Income Captions [Line Items]
Net income	$ 41,419	$ 39,365		$ 98,826	$ 97,875
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge	215	215		646	646
Foreign currency translation adjustment	(951)	(1,387)		(2,223)	(357)
Other comprehensive income (loss), net of tax	(736)	(1,172)		(1,577)	289
Comprehensive income	40,683	38,193		97,249	98,164
Parent [Member]
Condensed Statement of Income Captions [Line Items]
Net income	41,419	39,365		98,826	97,875
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge	215	215		646	646
Foreign currency translation adjustment	(951)	(1,387)		(2,223)	(357)
Other comprehensive income (loss), net of tax	(736)	(1,172)		(1,577)	289
Comprehensive income	40,683	38,193		97,249	98,164
Guarantor Subsidiaries [Member]
Condensed Statement of Income Captions [Line Items]
Net income	2,801	1,919	[1]	9,263	9,207
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge	0	0		0	0
Foreign currency translation adjustment	0	0		0	0
Other comprehensive income (loss), net of tax	0	0		0	0
Comprehensive income	2,801	1,919		9,263	9,207
Non-Guarantor Subsidiaries [Member]
Condensed Statement of Income Captions [Line Items]
Net income	6,465	8,234	[1]	21,490	26,735	[1]
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge	0	0		0	0
Foreign currency translation adjustment	(951)	(1,387)		(2,223)	(357)
Other comprehensive income (loss), net of tax	(951)	(1,387)		(2,223)	(357)
Comprehensive income	5,514	6,847	[1]	19,267	26,378	[1]
Eliminations [Member]
Condensed Statement of Income Captions [Line Items]
Net income	(9,266)	(10,153)	[1]	(30,753)	(35,942)	[1]
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge	0	0		0	0
Foreign currency translation adjustment	951	1,387		2,223	357
Other comprehensive income (loss), net of tax	951	1,387		2,223	357
Comprehensive income	(8,315)	(8,766)	[1]	(28,530)	(35,585)	[1]
Consolidated [Member]
Condensed Statement of Income Captions [Line Items]
Net income	41,419	39,365		98,826	97,875
Other comprehensive income (loss), net of tax:
Amortization of loss on cash flow hedge	215	215		646	646
Foreign currency translation adjustment	(951)	(1,387)		(2,223)	(357)
Other comprehensive income (loss), net of tax	(736)	(1,172)		(1,577)	289
Comprehensive income	$ 40,683	$ 38,193		$ 97,249	$ 98,164

[1] On July 21, 2015, the Company refinanced its existing $350 million senior secured credit facility ("Old Credit Facility") by entering into a new senior unsecured revolving credit agreement ("New Credit Facility"). As a result of this refinancing, certain guarantor subsidiaries under the Old Credit Facility have been released as a guarantor under the New Credit Facility. As a result, the following condensed consolidating financial statements for the prior year periods have been reclassified to reflect the current guarantors under the New Credit Facility.