Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended
	Jan. 31, 2013	Mar. 31, 2014
Significant Accounting Policies [Line Items]
Common stocks issued through underwritten public offering	9,200,000
Underwritten public offering amount per share	$ 20.13
Net proceeds from public issue, after deducting expenses	$ 173.6
Underwriting discounts and commissions and other estimated offering expenses	11.6
Marketable securities transferred from Level 2 to Level 1		$ 0
Marketable securities classified as cash equivalents, original maturity		90 days
Policy for marketable securities		90 days