Basis Of Presentation And New Accounting Standards (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Jan. 01, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Assets
Unbilled and other		$ 66,396		$ 66,396		$ 29,947
Other current assets		47,450		47,450		41,768
Liabilities
Accrued liabilities		84,431		84,431		71,680
Deferred tax liabilities		102,742		102,742		103,349
Equity
Retained earnings		396,781		396,781		$ 352,906
Statement of Operations
Net revenues		212,575	$ 163,260	581,462	$ 418,117
Income from operations		31,377	4,767	55,033	(7,888)
Income before income taxes		27,962	751	43,571	(21,645)
Income tax provision		841	(1,539)	1,226	(1,117)
Net income		27,121	$ 2,290	42,345	$ (20,528)
Pro Forma Without Adoption of ASC 606
Assets
Unbilled and other		67,263		67,263
Other current assets		46,104		46,104
Liabilities
Accrued liabilities		84,705		84,705
Deferred tax liabilities		102,584		102,584
Equity
Retained earnings		396,186		396,186
Statement of Operations
Net revenues		212,965		580,709
Income from operations		31,767		54,280
Income before income taxes		28,352		42,818
Income tax provision		923		1,068
Net income		27,429		41,750
Effect of Change | ASC 606
Assets
Unbilled and other		(867)		(867)
Other current assets		1,346		1,346
Liabilities
Accrued liabilities		(274)		(274)
Deferred tax liabilities		158		158
Equity
Retained earnings		595		595
Statement of Operations
Net revenues		(390)		753
Income from operations		(390)		753
Income before income taxes		(390)		753
Income tax provision		(82)		158
Net income		$ (308)		$ 595
Accumulated OCI | ASU No. 2018-02
Statement of Operations
Reclassification of net stranded tax benefits	$ (1,500)
Retained Earnings | ASU No. 2018-02
Statement of Operations
Reclassification of net stranded tax benefits	$ 1,500