Stockholders' and Mezzanine equity - Offering of Class A Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	3 Months Ended
	Sep. 12, 2016	Aug. 25, 2016	Sep. 12, 2016	Mar. 31, 2017	Dec. 31, 2016
Common Stock
Proceeds from sale of common stock				$ 2,829
Class A common stock
Common Stock
Shares issued				1,200,000
Common stock, par value (in dollars per share)				$ 0.001	$ 0.001
Proceeds from sale of common stock				$ 2,800
Class A common stock | Common Stock Underwriting Agreement
Common Stock
Shares issued		21,000,000
Proceeds from sale of common stock			$ 64,000
Class A common stock | Over-Allotment Option
Common Stock
Shares issued	3,150,000