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, 2018		34,606,760
Beginning balance at Dec. 31, 2018	$ 741,557	$ 346	$ 1,292,736	$ (3,985)	$ (547,540)
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)		262,919
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings	(1,718)	$ 3	(1,721)
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 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	9,407		9,407
Unrealized (losses) gains on securities, net of tax	953			953
Net loss	(243,569)				(243,569)
Ending balance (in shares) at Jun. 30, 2019		33,899,954
Ending balance at Jun. 30, 2019	493,751	$ 339	1,287,553	(3,032)	(791,109)
Beginning balance (in shares) at Mar. 31, 2019		33,746,828
Beginning balance at Mar. 31, 2019	609,305	$ 337	1,282,284	(3,376)	(669,940)
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)		48,051
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings	(114)	$ 1	(115)
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
Non-cash equity based compensation	4,534		4,534
Unrealized (losses) gains on securities, net of tax	344			344
Net loss	(121,169)				(121,169)
Ending balance (in shares) at Jun. 30, 2019		33,899,954
Ending balance at Jun. 30, 2019	$ 493,751	$ 339	1,287,553	(3,032)	(791,109)
Beginning balance (in shares) at Dec. 31, 2019	33,999,081	33,999,081
Beginning balance at Dec. 31, 2019	$ 279,816	$ 339	1,297,917	(3,239)	(1,015,201)
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)		368,090
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings	(1,327)	$ 4	(1,331)
Issuance of common stock under employee stock purchase plan (in shares)		96,202
Issuance of common stock under employee stock purchase plan	631	$ 1	630
Non-cash equity based compensation	5,879		5,879
Unrealized (losses) gains on securities, net of tax	275			275
Net loss	$ (35,952)				(35,952)
Ending balance (in shares) at Jun. 30, 2020	34,463,373	34,463,373
Ending balance at Jun. 30, 2020	$ 249,322	$ 344	1,303,095	(2,964)	(1,051,153)
Beginning balance (in shares) at Mar. 31, 2020		34,266,256
Beginning balance at Mar. 31, 2020	259,218	$ 342	1,300,572	(3,787)	(1,037,909)
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)		100,915
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings	(116)	$ 1	(117)
Issuance of common stock under employee stock purchase plan (in shares)		96,202
Issuance of common stock under employee stock purchase plan	631	$ 1	630
Non-cash equity based compensation	2,010		2,010
Unrealized (losses) gains on securities, net of tax	823			823
Net loss	$ (13,244)				(13,244)
Ending balance (in shares) at Jun. 30, 2020	34,463,373	34,463,373
Ending balance at Jun. 30, 2020	$ 249,322	$ 344	$ 1,303,095	$ (2,964)	$ (1,051,153)