Organization - Additional Information (Detail)	1 Months Ended			12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares	Mar. 31, 2015 USD ($) $ / shares shares	Oct. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2016 Segment
Organization And Nature Of Business [Line Items]
Number of operating segment | Segment				1
Follow on offering price per share | $ / shares	$ 48.00	$ 40.00	$ 26.00
Proceeds from offering and over-allotment option, gross			$ 175,200,000
Offering expenses			564,000
Proceeds from offering and over-allotment option, net			$ 174,600,000
Proceeds from offering and over-allotment option, net	$ 162,700,000	$ 108,400,000
Follow-on Offering
Organization And Nature Of Business [Line Items]
Stock issued during the period | shares	3,593,750	2,870,000	6,200,000
Underwriting discounts and commissions, net			$ 10,200,000
Underwriting discounts, commissions and offering expenses, net	$ 765,000	$ 358,000
Underwriters Overallotment Option
Organization And Nature Of Business [Line Items]
Stock issued during the period | shares	468,750	374,348	930,000