CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Earnings (Deficit)	Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity
Reclassification due to reincorporation		$ (264,505)	$ 264,505
Balances at December 31, 2015	$ 315,055	6	343,127	$ (28,024)	$ (54)
Balances at Dec. 31, 2015	315,055	$ 264,511	78,622	(28,024)	(54)
Balances (in shares) at Dec. 31, 2015		60,787,309
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options	6,693		6,693
Issuance of common stock upon exercise of options (in shares)		715,655
Issuance of common stock under employee stock purchase plan	3,258		3,258
Issuance of common stock under employee stock purchase plan (in shares)		201,264
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)		261,960
Stock-based compensation	17,172		17,172
Shares withheld for payment of employee's withholding tax liability	(3,342)		(3,342)
Windfall tax benefit	637		637
Net income (loss)	(88,720)			(88,720)
Unrealized gain on available-for-sale securities	35				35
Balances at Dec. 31, 2016	250,788	$ 6	367,545	(116,744)	(19)
Balances (in shares) at Dec. 31, 2016		61,966,188
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options	$ 6,979		6,979
Issuance of common stock upon exercise of options (in shares)	1,000,892	1,001,142
Issuance of common stock under employee stock purchase plan	$ 1,960		1,960
Issuance of common stock under employee stock purchase plan (in shares)		261,569
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)		171,449
Stock-based compensation	13,016		13,016
Shares withheld for payment of employee's withholding tax liability	(753)		(753)
Net income (loss)	(102,496)			(102,496)
Unrealized gain on available-for-sale securities	14				14
Balances at Dec. 31, 2017	$ 169,508	$ 6	389,015	(219,508)	(5)
Balances (in shares) at Dec. 31, 2017	63,400,348	63,400,000
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options	$ 1,493		1,493
Issuance of common stock upon exercise of options (in shares)	278,000	278,000
Issuance of common stock under employee stock purchase plan	$ 527		527
Issuance of common stock under employee stock purchase plan (in shares)		107,000
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)		400,000
Stock-based compensation	12,585		12,585
Shares withheld for payment of employee's withholding tax liability	(686)		(686)
Net income (loss)	36,908			36,908
Unrealized gain on available-for-sale securities	0
Balances at Dec. 31, 2018	$ 220,335	$ 6	$ 402,934	$ (182,600)	$ (5)
Balances (in shares) at Dec. 31, 2018	64,185,224	64,185,000