CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2017		34,083,112
Beginning balance at Dec. 31, 2017	$ 790,244	$ 341	$ 1,271,628	$ (3,908)	$ (477,817)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings (in shares)		439,845
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings	4	$ 4
Non-cash equity based compensation	14,599		14,599
Unrealized gains (losses) on securities, net of tax	(253)			(253)
Net loss	(43,484)				(43,484)
Ending balance (in shares) at Sep. 30, 2018		34,522,957
Ending balance at Sep. 30, 2018	762,246	$ 345	1,286,227	(4,161)	(520,165)
Beginning balance (in shares) at Jun. 30, 2018		34,390,068
Beginning balance at Jun. 30, 2018	726,903	$ 344	1,281,858	(4,295)	(551,004)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings (in shares)		132,889
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings	893	$ 1	892
Non-cash equity based compensation	3,477		3,477
Unrealized gains (losses) on securities, net of tax	134			134
Net loss	30,839				30,839
Ending balance (in shares) at Sep. 30, 2018		34,522,957
Ending balance at Sep. 30, 2018	$ 762,246	$ 345	1,286,227	(4,161)	(520,165)
Beginning balance (in shares) at Dec. 31, 2018	34,606,760	34,606,760
Beginning balance at Dec. 31, 2018	$ 746,655	$ 346	1,292,736	(3,985)	(542,442)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings (in shares)		278,474
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings	(1,787)	$ 3	(1,790)
Issuance of common stock under employee stock purchase plan (in shares)		105,075
Issuance of common stock under employee stock purchase plan	851	$ 1	850
Repurchase of common stock pursuant to the 2016 share repurchase program (in shares)		(1,074,800)
Repurchase of common stock pursuant to the share repurchase program	(13,730)	$ (11)	(13,719)
Non-cash equity based compensation	14,381		14,381
Unrealized gains (losses) on securities, net of tax	786			786
Net loss	$ (266,528)				(266,528)
Ending balance (in shares) at Sep. 30, 2019	33,915,509	33,915,509
Ending balance at Sep. 30, 2019	$ 480,628	$ 339	1,292,458	(3,199)	(808,970)
Beginning balance (in shares) at Jun. 30, 2019		33,899,954
Beginning balance at Jun. 30, 2019	499,507	$ 339	1,287,553	(3,032)	(785,353)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings (in shares)		15,555
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings	(69)		(69)
Non-cash equity based compensation	4,974		4,974
Unrealized gains (losses) on securities, net of tax	(167)			(167)
Net loss	$ (23,617)				(23,617)
Ending balance (in shares) at Sep. 30, 2019	33,915,509	33,915,509
Ending balance at Sep. 30, 2019	$ 480,628	$ 339	$ 1,292,458	$ (3,199)	$ (808,970)