Description of Business (Details) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Jul. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2017 segment	Dec. 31, 2015 shares
Number of operating segments | segment		1
Common stock
Initial public offering (in shares)			10,900,000
IPO | Common stock
Initial public offering (in shares)	10,900,000
Initial public offering price (in dollars per share) | $ / shares	$ 18.00
Proceeds from initial public offering, net of offering costs | $	$ 178.5