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	9 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares
Number of Shares (in thousands)
Beginning balance outstanding (in shares) | shares	1,123
Awarded (in shares) | shares	2,130
Released (in shares) | shares	(334)
Forfeited (in shares) | shares	(234)
Non-vested and outstanding at end of period (in shares) | shares	2,685
Expected to vest (in shares) | shares	1,878
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	16.35
Released (in dollars per share) | $ / shares	9.04
Forfeited (in dollars per share) | $ / shares	10.42
Non-vested and outstanding at end of period (in dollars per share) | $ / shares	14.71
Expected to vest (in dollars per share) | $ / shares	$ 13.93
Aggregate Fair Value (in thousands)
Non-vested and outstanding at September 30, 2018 | $	$ 69,673
Expected to vest | $	$ 48,741