Follow-On Public Offering - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Jan. 16, 2014
Equity [Abstract]
Follow-on public offering shares			6,072,000
Follow-on public offering shares sold			747,500
Follow-on public offering selling shares sold			5,324,500
Follow-on public offering shares price			$ 35.50
Offering closed date	Jan. 23, 2014
Proceeds from follow-on public offering, net of expenses	$ 0	$ 24,846