Stockholders' Equity - Additional Information (Detail) - Follow On Public Offering - USD ($) $ / shares in Units, $ in Millions	1 Months Ended
	Mar. 31, 2015	Oct. 31, 2014
Shareholders Equity [Line Items]
Common stock, shares issued	4,945,000	4,542,500
Common stock, issue price	$ 35.00	$ 19.00
Proceeds from issuing of shares	$ 162.2	$ 80.8
Underwriting discounts and commissions	10.4	5.2
Offering costs	$ 0.5	$ 0.4