Equity Financing - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	1 Months Ended		9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2016
Equity [Abstract]
Common stock issued	5.8	2.1
Common stock average price per share	$ 59.75	$ 17.84	$ 59.75
Net proceeds from issue of common stock	$ 327,400	$ 37,300	$ 364,951
Commission and offering expenses	$ 17,600	$ 200
Underwriting discount and commission per share		$ 1.60