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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5047-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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=115993241&loc=d3e301413-122809

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-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=109197908&loc=d3e5070-113901

Summary of Significant Accounting Policies - Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Income (Loss) Per Share
Anti-dilutive securities (in shares)									1,884,000	1,291,000
Stock-Based Compensation
Stock-based compensation expense									$ 20,548	$ 13,651	$ 7,848
Basic numerator:
Net income (loss) attributable to common stockholders									$ (70,409)	$ (38,486)	$ 45,125
Denominator:
Weighted average common shares outstanding, basic									53,942,116	46,817,756	41,267,329
Net income (loss) per common share, basic (in dollars per share)	$ (0.32)	$ 0.06	$ (0.46)	$ (0.62)	$ 0.16	$ (0.48)	$ (0.17)	$ (0.33)	$ (1.31)	$ (0.82)	$ 1.09
Diluted numerator:
Net income (loss) attributable to common stockholders for diluted net income (loss) per share									$ (70,409)	$ (38,486)	$ 45,125
Denominator
Weighted average common shares outstanding, basic									53,942,116	46,817,756	41,267,329
Dilutive effect of employee stock options and ESPP											1,121,538
Weighted average common shares outstanding, diluted									53,942,116	46,817,756	42,388,867
Net income (loss) per common share, diluted (in dollars per share)	$ (0.32)	$ 0.05	$ (0.46)	$ (0.62)	$ 0.15	$ (0.48)	$ (0.17)	$ (0.33)	$ (1.31)	$ (0.82)	$ 1.07
Employee stock options
Net Income (Loss) Per Share
Anti-dilutive securities (in shares)									1,881,000	1,291,000
ESPP
Net Income (Loss) Per Share
Anti-dilutive securities (in shares)									3,000
Stock-Based Compensation
Stock-based compensation expense									$ 700	$ 500	$ 400