Stockholders' (Deficit) Equity - Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended			12 Months Ended
	May 07, 2018	Feb. 28, 2017	Oct. 31, 2016	Mar. 31, 2014	Dec. 31, 2017	Jun. 30, 2018	Mar. 31, 2018
Stockholders' Equity
Shares Authorized					76,894,620	10,000,000
Shares Issued					76,235,050	0
Shares Outstanding					76,235,050	0
Carrying Value					$ 119,106
Dividend rate (as a percent)					8.00%
Convertible preferred stock
Stockholders' Equity
Shares Authorized					76,894,620
Shares Issued					76,235,050
Carrying Value					$ 119,106
Series A convertible preferred stock
Stockholders' Equity
Shares Authorized					5,375,507
Shares Issued					5,375,507
Shares Outstanding					5,375,507
Carrying Value					$ 5,037
Liquidation Preference per Share					$ 1.00
8% Dividend per Share					0.08
Conversion Price per Share					$ 6.65
Shares issue price (in dollars per share)							$ 1.00
Number of common shares called by each convertible preferred share							0.1504
Series B convertible preferred stock
Stockholders' Equity
Shares Authorized					8,706,909
Shares Issued					8,706,909
Shares Outstanding					8,706,909
Carrying Value					$ 15,913
Liquidation Preference per Share					$ 1.84
8% Dividend per Share					0.15
Conversion Price per Share					$ 9.91
Shares issue price (in dollars per share)							$ 1.84
Number of common shares called by each convertible preferred share							0.1855
Series C convertible preferred stock
Stockholders' Equity
Shares Authorized					14,091,589
Shares Issued					13,829,906
Shares Outstanding					13,829,906
Carrying Value					$ 14,949
Liquidation Preference per Share					$ 1.07
8% Dividend per Share					0.09
Conversion Price per Share					$ 7.12
Shares issue price (in dollars per share)							$ 1.07
Number of common shares called by each convertible preferred share							0.1504
Series D convertible preferred stock
Stockholders' Equity
Shares Authorized					5,683,292
Shares Issued					5,683,292
Shares Outstanding					5,683,292
Carrying Value					$ 6,043
Liquidation Preference per Share					$ 1.07
8% Dividend per Share					0.09
Conversion Price per Share					$ 7.12
Shares issue price (in dollars per share)							$ 1.07
Number of common shares called by each convertible preferred share							0.1504
Series E convertible preferred stock
Stockholders' Equity
Shares Authorized					15,373,091
Shares Issued					15,267,175
Shares Outstanding					15,267,175
Carrying Value					$ 39,848
Liquidation Preference per Share					$ 2.62
8% Dividend per Share					0.21
Conversion Price per Share					$ 15.16
Net proceeds from issuance of convertible preferred stock				$ 39,800
Shares issued during the period				15,267,175
Shares issue price (in dollars per share)				$ 2.62
Number of common shares called by each convertible preferred share				0.1728
Series F convertible preferred stock
Stockholders' Equity
Shares Authorized					27,664,232
Shares Issued					27,372,261
Shares Outstanding					27,372,261
Carrying Value					$ 37,316
Liquidation Preference per Share					$ 1.37
8% Dividend per Share					0.11
Conversion Price per Share					$ 9.11
Net proceeds from issuance of convertible preferred stock		$ 25,000	$ 12,300
Shares issued during the period		18,248,177	9,124,084
Shares issue price (in dollars per share)		$ 1.37	$ 1.37
IPO | Convertible preferred stock
Stockholders' Equity
Number of shares converted	76,235,050
Value of shares converted	$ 119,100
IPO | Common Stock
Stockholders' Equity
Shares issued upon conversion	12,111,706
Shares issued during the period	7,762,500
Shares issue price (in dollars per share)	$ 16.00