Significant Accounting Policies Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) days	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Accounting Policies [Abstract]
Debt issuance costs reclassified as adjustments to carrying cost of debt		$ 13,900
Allowance for doubtful accounts receivable, current	$ 2,900	4,000
Unbilled receivables,current	$ 80,400	74,500
Number of days or less of maturity to be considered cash equivalent | days	90
Excess tax benefits, share-based compensation cost	$ 1,800	$ 1,800	$ (100)
Cumulative effect of new accounting principle in period of adoption	2,603
Retained Earnings
Cumulative effect of new accounting principle in period of adoption	$ 2,603