CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS’ EQUITY (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Earnings (Deficit)	Accumulated Other Comprehensive Loss
Balances (in shares) at Dec. 31, 2017		63,400
Balances at Dec. 31, 2017	$ 169,508	$ 6	$ 389,015	$ (219,508)	$ (5)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options (in shares)		120
Issuance of common stock upon exercise of options	636		636
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)		33
Stock-based compensation	2,234		2,234
Shares withheld for payment of employee's withholding tax liability	(114)		(114)
Net (loss) income	33,824			33,824
Unrealized gain on available-for-sale securities	2				2
Balances (in shares) at Mar. 31, 2018		63,553
Balances at Mar. 31, 2018	206,090	$ 6	391,771	(185,684)	(3)
Balances (in shares) at Dec. 31, 2017		63,400
Balances at Dec. 31, 2017	169,508	$ 6	389,015	(219,508)	(5)
Increase (Decrease) in Stockholders' Equity
Net (loss) income	12,776
Unrealized gain on available-for-sale securities	1
Balances (in shares) at Jun. 30, 2018		63,902
Balances at Jun. 30, 2018	191,206	$ 6	397,936	(206,732)	(4)
Balances (in shares) at Mar. 31, 2018		63,553
Balances at Mar. 31, 2018	206,090	$ 6	391,771	(185,684)	(3)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options (in shares)		108
Issuance of common stock upon exercise of options	667		667
Issuance of common stock under employee stock purchase plan (in shares)		72
Issuance of common stock under employee stock purchase plan	381		381
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)		169
Stock-based compensation	5,270		5,270
Shares withheld for payment of employee's withholding tax liability	(153)		(153)
Net (loss) income	(21,048)			(21,048)
Unrealized gain on available-for-sale securities	(1)				(1)
Balances (in shares) at Jun. 30, 2018		63,902
Balances at Jun. 30, 2018	191,206	$ 6	397,936	(206,732)	(4)
Balances (in shares) at Dec. 31, 2018		64,185
Balances at Dec. 31, 2018	220,335	$ 6	402,934	(182,600)	(5)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options (in shares)		14
Issuance of common stock upon exercise of options	25		25
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)		132
Stock-based compensation	2,702		2,702
Shares withheld for payment of employee's withholding tax liability	(216)		(216)
Net (loss) income	(14,301)			(14,301)
Balances (in shares) at Mar. 31, 2019		64,331
Balances at Mar. 31, 2019	208,545	$ 6	405,445	(196,901)	(5)
Balances (in shares) at Dec. 31, 2018		64,185
Balances at Dec. 31, 2018	220,335	$ 6	402,934	(182,600)	(5)
Increase (Decrease) in Stockholders' Equity
Net (loss) income	(27,906)
Unrealized gain on available-for-sale securities	0
Balances (in shares) at Jun. 30, 2019		64,821
Balances at Jun. 30, 2019	197,439	$ 6	407,944	(210,506)	(5)
Balances (in shares) at Mar. 31, 2019		64,331
Balances at Mar. 31, 2019	208,545	$ 6	405,445	(196,901)	(5)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under employee stock purchase plan (in shares)		64
Issuance of common stock under employee stock purchase plan	158		158
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)		426
Stock-based compensation	2,634		2,634
Shares withheld for payment of employee's withholding tax liability	(293)		(293)
Net (loss) income	(13,605)			(13,605)
Unrealized gain on available-for-sale securities	0
Balances (in shares) at Jun. 30, 2019		64,821
Balances at Jun. 30, 2019	$ 197,439	$ 6	$ 407,944	$ (210,506)	$ (5)