CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (shares) at Dec. 31, 2014		25,599,550
Beginning balance at Dec. 31, 2014	$ 459,953	$ 256	$ 793,757	$ (3,617)	$ (330,443)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued in connection with financings, net of issuance costs of $24.7 million (shares)		8,196,362
Shares issued in connection with financings, net of issuance costs of $24.7 million	407,477	$ 82	407,395
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings (shares)		937,205
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings	15,406	$ 9	15,397
Non-cash equity-based compensation	17,237		17,237
Unrealized losses on securities, net of tax	(588)			(588)
Net (loss) income	32,779				32,779
Ending balance (shares) at Dec. 31, 2015		34,733,117
Ending balance at Dec. 31, 2015	932,264	$ 347	1,233,786	(4,205)	(297,664)
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 (shares)		355,450
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings	230	$ 3	227
Non-cash equity-based compensation	22,543		22,543
Unrealized losses on securities, net of tax	367			367
Net (loss) income	(2,483)				(2,483)
Repurchase of common stock pursuant to the 2016 Share Repurchase Program (shares)		(831,744)
Repurchase of common stock pursuant to the 2016 Share Repurchase Program	(20,000)	$ (8)	(19,992)
Issuance of common stock under employee stock purchase plan (shares)		79,324
Issuance of common stock under employee stock purchase plan	$ 1,468	$ 1	1,467
Repurchase and retirement of common stock pursuant to the 2016 Share Repurchase Program (shares)	(831,744)
Repurchase and retirement of common stock pursuant to the 2016 Share Repurchase Program	$ (20,000)
Ending balance (shares) at Dec. 31, 2016		34,336,147
Ending balance at Dec. 31, 2016	934,389	$ 343	1,238,031	(3,838)	(300,147)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of previously unrecognized excess tax benefits related to stock compensation	21,558
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings (shares)		392,651
Net shares issued in connection with the exercise of stock options and vesting of restricted stock units, net of withholdings	(1,267)	$ 5	(1,272)
Non-cash equity-based compensation	23,664		23,664
Unrealized losses on securities, net of tax	(70)			(70)
Net (loss) income	(199,228)				(199,228)
Issuance of common stock under employee stock purchase plan (shares)		120,580
Issuance of common stock under employee stock purchase plan	1,594	$ 1	1,593
Settlement of warrants	323		323
Equity component of the 2022 Convertible Notes, net of issuance costs and taxes	43,236		43,236
Equity component of debt repurchase	(27,988)		(27,988)
Shares issued in connection with Endoceutics License Agreement (shares)		600,000
Shares issued in connection with Endoceutics License Agreement	$ 13,500	$ 6	13,494
Repurchase and retirement of common stock pursuant to the 2016 Share Repurchase Program (shares)	(1,366,266)	(1,366,266)
Repurchase and retirement of common stock pursuant to the 2016 Share Repurchase Program	$ (19,467)	$ (14)	(19,453)
Ending balance (shares) at Dec. 31, 2017		34,083,112
Ending balance at Dec. 31, 2017	$ 790,244	$ 341	$ 1,271,628	$ (3,908)	(477,817)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of previously unrecognized excess tax benefits related to stock compensation					$ 21,558