Common Stock - Additional Information (Detail) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Aug. 31, 2012	Oct. 07, 2011	Jul. 30, 2013
Class of Stock [Line Items]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	40,635,233	40,627,131
Common stock, shares outstanding	34,056,468	34,048,366
Purchase of common stock in open market, shares		2,614,748
Purchase of common stock in open market, value		$ 51,000,000	$ 28,125,000
Decrease in stockholders' equity		51,000,000
Expiration date of stock repurchase program	Dec. 15, 2014
Program One [Member]
Class of Stock [Line Items]
Common stock repurchase, maximum amount				60,000,000	35,000,000
Common stock purchase by an additional amount				25,000,000
Program Two [Member]
Class of Stock [Line Items]
Common stock repurchase, maximum amount						$ 100,000,000
Program Two [Member] | Minimum [Member]
Class of Stock [Line Items]
New stock repurchase program, effective date	Aug. 05, 2013
Program Two [Member] | Maximum [Member]
Class of Stock [Line Items]
New stock repurchase program, effective date	Dec. 15, 2014