Stockholders' Equity (Summary of Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Apr. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Options
Outstanding Options, Beginning of period				9,763,485
Options granted				1,789,254
Options exercised				(1,473,323)
Options cancelled				(84,203)
Options expired				(1,108,177)
Outstanding Options, End of period		8,887,036		8,887,036
Exercisable at the end of period		6,029,545		6,029,545
Weighted-Average Exercise Price
Outstanding Exercise Price (in dollars per share)				$ 15.26
Options granted (in dollars per share)				13.52
Options exercised (in dollars per share)				14.22
Options cancelled (in dollars per share)				16.53
Options expired (in dollars per share)				16.45
Outstanding Exercise Price (in dollars per share)		$ 14.92		14.92
Exercisable at the end of period (in dollars per share)		$ 14.31		$ 14.31
Additional Disclosures
Outstanding Contractual Term (in Years)				5 years 7 months 24 days
Outstanding Intrinsic Value		$ 66,980		$ 66,980
Exercisable remaining contractual term (in Years)				4 years 4 months 28 days
Exercisable aggregate intrinsic value		49,123		$ 49,123
Allocated share based compensation		6,513	$ 4,032	11,795	$ 8,706
Employee Stock Option
Additional Disclosures
Allocated share based compensation		2,600	$ 1,800	5,200	$ 4,200
Employee Stock Option | President, General Counsel and member of board of directors
Additional Disclosures
Allocated share based compensation		$ 700		$ 700
Vesting (percent)	80.00%