Summary of Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Royalty Revenue
Number of types of royalty revenue streams	2
Stock-Based Compensation and Equity Incentive Plans
Discount from the fair market value (as a percent)	15.00%
Cash and Cash Equivalents
Maximum original maturity of cash equivalents (in months)	3 months
Minimum
Intangible Assets
Useful life (in years)	1 year	1 year
Maximum
Intangible Assets
Useful life (in years)	10 years	10 years