Income Taxes - Reconciliation of Effective Tax Rate (Details)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
U.S. federal statutory tax rate	(21.00%)	(35.00%)
State income taxes, net of federal benefit	(37.00%)	(2.20%)
Non-U.S. income taxed at different rates	102.00%	0.50%
Reduction in tax benefit related to stock-based awards	(217.70%)	6.20%
Non-deductible expenses	(44.20%)	(0.70%)
Research and development credit	132.10%	1.10%
Other	(15.10%)	(0.00%)
Effective income tax rate	(100.90%)	(30.10%)