Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Royalty liability	$ 482,300
Discount rate used to calculate present value of royalty payments	5.70%
Money market funds
Cash equivalents	$ 81,479	$ 81,225
Quoted Prices in active markets (Level 1) \| Money market funds
Cash equivalents	$ 81,479	$ 81,225

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant