Stockholders' Equity (Summary of Restricted Stock Unit Activity and Weighted Average Exercise Price) (Details) - Restricted Stock Units (RSUs) [Member] $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
Number of Shares (in thousands)
Beginning balance outstanding (in shares) | shares	1,123
Awarded (in shares) | shares	724
Released (in shares) | shares	(124)
Forfeited (in shares) | shares	(76)
Non-vested and outstanding at end of period (in shares) | shares	1,647
Expected to vest (in shares) | shares	1,298
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	13.12
Released (in dollars per share) | $ / shares	9.73
Forfeited (in dollars per share) | $ / shares	7.77
Non-vested and outstanding at end of period (in dollars per share) | $ / shares	10.83
Expected to vest (in dollars per share) | $ / shares	$ 10.86
Aggregate Fair Value (in thousands)
Non-vested and outstanding at March 31, 2018 | $	$ 23,935
Expected to vest | $	$ 21,219