Income Taxes - Narrative (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
Cumulative effect of new accounting principle in period of adoption	$ 6,200
Decrease in valuation allowance		$ 11,600
Valuation allowance		(159,737)			$ (171,315)
Provisional income tax benefit from change in tax rate due to Tax Cuts and Jobs Act of 2017		53,342
Gross unrecognized tax benefits		7,940			6,678	$ 5,116	$ 4,064
Unrecognized tax benefits, if recognized, would not impact the company's effective tax rate		$ 7,800			$ 6,600
Minimum number of years for which jobs must be maintained		5 years
Job creation tax award		$ 1,100
Revenue from job creation tax award recognized as other income		200
Federal
Income Tax Contingency [Line Items]
Operating loss carryforwards utilized			$ 190,900	$ 26,300
Net operating loss carryforwards		369,300
Research and development and other credit carryforwards		12,000
State
Income Tax Contingency [Line Items]
Net operating loss carryforwards		343,500
Research and development and other credit carryforwards		$ 35,000