Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended		12 Months Ended
	Feb. 28, 2015	Feb. 28, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class of Stock [Line Items]
Proceeds from common stock issuance	$ 270,700	$ 133,200	$ 276,992	$ 138,731	$ 5,302
Common Stock
Class of Stock [Line Items]
Common stock issued	8,000	8,000	7,986	8,000
Common stock, offering price	$ 36.00	$ 17.75
February Two Thousand Fourteen Shelf Registration [Member]
Class of Stock [Line Items]
Common stock issued			16,000