Redeemable Convertible Preferred Stock (Summary of Activity) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, Preferred stock issued and outstanding	$ 0	$ 118,343	$ 53,226
Redemption of preferred stock			(1,028)
Issuance of preferred stock		76,985	58,675
Exercise of preferred stock warrants		13,292
Accretion of dividends on preferred stock	0	12,884	7,470
Conversion of preferred stock to common stock in connection with initial public offering		(221,504)
Ending balance, Preferred stock issued and outstanding		0	$ 118,343
Number of shares redeemed (shares)			1,525,096
Differential between redemption price and carrying value	$ 0	0	$ 5,254
Series A
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, Preferred stock issued and outstanding		2,559	3,250
Redemption of preferred stock			(835)
Issuance of preferred stock		0	0
Exercise of preferred stock warrants		0
Accretion of dividends on preferred stock		124	144
Conversion of preferred stock to common stock in connection with initial public offering		(2,683)
Ending balance, Preferred stock issued and outstanding			$ 2,559
Number of shares redeemed (shares)			1,514,698
Series B
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, Preferred stock issued and outstanding		22,918	$ 21,838
Redemption of preferred stock			(193)
Issuance of preferred stock		0	0
Exercise of preferred stock warrants		5,982
Accretion of dividends on preferred stock		1,240	1,273
Conversion of preferred stock to common stock in connection with initial public offering		(30,140)
Ending balance, Preferred stock issued and outstanding			$ 22,918
Number of shares redeemed (shares)			91,460
Series C
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, Preferred stock issued and outstanding		24,749	$ 23,113
Redemption of preferred stock			0
Issuance of preferred stock		0	0
Exercise of preferred stock warrants		0
Accretion of dividends on preferred stock		1,570	1,636
Conversion of preferred stock to common stock in connection with initial public offering		(26,319)
Ending balance, Preferred stock issued and outstanding			24,749
Series C-1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, Preferred stock issued and outstanding		5,401	5,025
Redemption of preferred stock			0
Issuance of preferred stock		0	0
Exercise of preferred stock warrants		7,225
Accretion of dividends on preferred stock		413	376
Conversion of preferred stock to common stock in connection with initial public offering		(13,039)
Ending balance, Preferred stock issued and outstanding			5,401
Series D
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, Preferred stock issued and outstanding		62,716	0
Redemption of preferred stock			0
Issuance of preferred stock		0	58,675
Exercise of preferred stock warrants		0
Accretion of dividends on preferred stock		4,619	4,041
Conversion of preferred stock to common stock in connection with initial public offering		(67,335)
Ending balance, Preferred stock issued and outstanding			62,716
Series E
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, Preferred stock issued and outstanding		0	0
Redemption of preferred stock			0
Issuance of preferred stock		76,985	0
Exercise of preferred stock warrants		85
Accretion of dividends on preferred stock		4,918	0
Conversion of preferred stock to common stock in connection with initial public offering		$ (81,988)
Ending balance, Preferred stock issued and outstanding			$ 0