Income Taxes - Reconciliation of Effective Tax Rate (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
U.S. federal statutory tax rate	(21.00%)	(35.00%)	(21.00%)	(35.00%)
State income taxes, net of federal benefit	(2.30%)	14.30%	0.30%	6.70%
Non-U.S. income taxed at different rates	(4.60%)	8.90%	(0.70%)	5.40%
Reduction in tax benefit related to stock-based awards	0.80%	15.80%	1.40%	14.10%
Non-deductible expenses	6.30%	8.50%	10.10%	4.50%
Research and development credit	4.70%	(13.50%)	(0.40%)	(7.10%)
Valuation allowance	3.70%	(0.00%)	34.20%	(0.00%)
Other	4.70%	1.50%	0.50%	(1.00%)
Effective income tax rate	(7.70%)	0.50%	24.40%	(12.40%)