Stockholders' Equity (Summary of Restricted Stock Unit Activity and Weighted Average Exercise Price) (Details) - Restricted Stock Units (RSUs) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares
Number of Shares (in thousands)
Beginning balance outstanding (in shares) | shares	1,123
Awarded (in shares) | shares	1,843
Released (in shares) | shares	(251)
Forfeited (in shares) | shares	(107)
Non-vested and outstanding at end of period (in shares) | shares	2,608
Expected to vest (in shares) | shares	1,798
Weighted Average Grant Date Fair Value (usd per share)
Beginning balance outstanding (in dollars per share) | $ / shares	$ 9.03
Awarded (in dollars per share) | $ / shares	15.13
Released (in dollars per share) | $ / shares	9.05
Forfeited (in dollars per share) | $ / shares	8.02
Non-vested and outstanding at end of period (in dollars per share) | $ / shares	13.38
Expected to vest (in dollars per share) | $ / shares	$ 12.80
Aggregate Fair Value (in thousands)
Non-vested and outstanding at June 30, 2018 | $	$ 55,026
Expected to vest | $	$ 37,936