Common stock and preferred stock - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Common stock, shares authorized	125,000,000	125,000,000
Common stock voting rights	Common stock are entitled to one vote per share
Issuing of shares	5,000,000	5,000,000
Shares of preferred stock issued	0	0
Shares of preferred stock outstanding	0	0