Summary Of Significant Accounting Policies - New Accounting Standards (Details) - USD ($) $ in Thousands			3 Months Ended								12 Months Ended
	Jan. 01, 2019	Jan. 01, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Unbilled and other			$ 51,943				$ 29,947				$ 51,943	$ 29,947
Other current assets			51,594				41,768				51,594	41,768
Liabilities
Accrued liabilities			85,594				71,680				85,594	71,680
Deferred tax liabilities			105,862				103,349				105,862	103,349
Equity
Retained earnings			383,034				352,906				383,034	352,906
Statement of Operations
Net revenues			158,356	$ 212,575	$ 204,625	$ 164,262	163,266	$ 163,260	$ 150,329	$ 104,528	739,818	581,383	$ 487,582
Income (loss) from operations											51,543	(1,130)	(63,235)
Income (loss) before income taxes											30,998	(20,372)	(93,915)
Income tax provision (benefit)											2,400	(50,424)	(12,470)
Net income (loss)			(13,747)	$ 27,121	$ 17,784	$ (2,560)	50,580	$ 2,290	$ (6,403)	$ (16,415)	28,598	30,052	(81,445)
Reclassification of net stranded tax effect from accumulated OCI to retained earnings											0
Deferred gain on sale and leaseback transaction			5,052				$ 5,838				5,052	5,838
AOCI
Statement of Operations
Reclassification of net stranded tax effect from accumulated OCI to retained earnings											1,530
Retained Earnings
Statement of Operations
Net income (loss)											28,598	$ 30,052	$ (81,445)
Reclassification of net stranded tax effect from accumulated OCI to retained earnings											(1,530)
Pro Forma Without Adoption of ASC 606
Assets
Unbilled and other			57,772								57,772
Other current assets			45,765								45,765
Liabilities
Accrued liabilities			85,491								85,491
Deferred tax liabilities			105,884								105,884
Equity
Retained earnings			383,115								383,115
Statement of Operations
Net revenues											739,921
Income (loss) from operations											51,646
Income (loss) before income taxes											31,101
Income tax provision (benefit)											2,422
Net income (loss)											28,679
ASC 606 | Effect of Change
Assets
Unbilled and other			(5,829)								(5,829)
Other current assets			5,829								5,829
Liabilities
Accrued liabilities			103								103
Deferred tax liabilities			(22)								(22)
Equity
Retained earnings			$ (81)								(81)
Statement of Operations
Net revenues											(103)
Income (loss) from operations											(103)
Income (loss) before income taxes											(103)
Income tax provision (benefit)											(22)
Net income (loss)											$ (81)
ASU No. 2018-02 | AOCI
Statement of Operations
Reclassification of net stranded tax effect from accumulated OCI to retained earnings		$ 1,500
ASU No. 2018-02 | Retained Earnings
Statement of Operations
Reclassification of net stranded tax effect from accumulated OCI to retained earnings		$ (1,500)
ASC 842 | Minimum | Scenario, Forecast
Statement of Operations
Increases in assets and liabilities	$ 250,000
ASC 842 | Maximum | Scenario, Forecast
Statement of Operations
Increases in assets and liabilities	270,000
ASC 842 | Retained Earnings | Scenario, Forecast
Statement of Operations
Deferred gain on sale and leaseback transaction	$ 5,100