Organization - Additional Information (Detail) $ / shares in Units, $ in Millions	1 Months Ended	9 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) Segment $ / shares
Organization And Nature Of Business [Line Items]
Number of operating segment | Segment		1
Follow on offering price per share | $ / shares	$ 55.00	$ 55.00
Proceeds from offering and over-allotment option, gross	$ 380.6
Offering expenses	0.7	$ 0.7
Proceeds from offering and over-allotment option, net	$ 379.9
Follow-on Offering
Organization And Nature Of Business [Line Items]
Stock issued during the period | shares	7,302,500
Underwriting discounts and commissions, net	$ 21.1
Underwriters Overallotment Option
Organization And Nature Of Business [Line Items]
Stock issued during the period | shares	952,500