Capital Stock - Summary of Outstanding Convertible Preferred Stock (Details) - USD ($) $ in Thousands	Dec. 31, 2017	May 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class Of Stock [Line Items]
Temporary equity, aggregate liquidation preference		$ 42,575
Series B-1 Convertible Preferred Stock
Class Of Stock [Line Items]
Temporary equity, shares authorized	4,773,000	4,773,000	4,773,000
Temporary equity, shares issued	0	3,848,023	3,848,023
Temporary equity, shares outstanding	0	3,848,023	3,848,023	3,848,023	3,507,117
Temporary equity, aggregate liquidation preference		$ 22,575	$ 22,575
Series A-2 Convertible Preferred Stock
Class Of Stock [Line Items]
Temporary equity, shares authorized	1,177,000	1,177,000	1,177,000
Temporary equity, shares issued	0	1,176,423	1,176,423
Temporary equity, shares outstanding	0	1,176,423	1,176,423	1,176,423	1,176,423
Temporary equity, aggregate liquidation preference		$ 20,000	$ 20,000