Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

Summary of Significant Accounting Policies - Net Loss Per Share (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Income (Loss) Per Share
Anti-dilutive securities (in shares)									1,291,000		1,356,000
Stock-Based Compensation
Stock-based compensation expense									$ 13,651,000	$ 7,848,000	$ 4,869,000
Basic numerator:
Net income (loss) attributable to common stockholders for basic net income (loss) per share									$ (48,925,000)	$ 23,625,000	$ (17,592,000)
Denominator:
Weighted average common shares outstanding, basic									46,817,756	41,267,329	39,015,131
Net income (loss) per common share, basic (in dollars per share)	$ (0.25)	$ (0.33)	$ (0.15)	$ (0.31)	$ (0.21)	$ (0.20)	$ 1.16	$ (0.16)	$ (1.05)	$ 0.57	$ (0.45)
Diluted numerator:
Net income (loss) attributable to common stockholders for diluted net income (loss) per share									$ (48,925,000)	$ 23,625,000	$ (17,592,000)
Denominator
Weighted average common shares outstanding, basic									46,817,756	41,267,329	39,015,131
Dilutive effect of conversion of convertible preferred stock										1,121,538
Weighted average common shares outstanding, diluted									46,817,756	42,388,867	39,015,131
Net income (loss) per common share, diluted (in dollars per share)	$ (0.25)	$ (0.33)	$ (0.15)	$ (0.31)	$ (0.21)	$ (0.20)	$ 1.13	$ (0.16)	$ (1.05)	$ 0.56	$ (0.45)
Employee stock options
Net Income (Loss) Per Share
Anti-dilutive securities (in shares)									1,291,000		1,281,000
Employee Stock Purchase Plan
Net Income (Loss) Per Share
Anti-dilutive securities (in shares)											75,000
Stock-Based Compensation
Stock-based compensation expense									$ 498,000	$ 378,000