Stockholders' Equity - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended
	Nov. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Class of Stock [Line Items]
Common stock, shares authorized		100,000,000	100,000,000
Common stock, shares issued		82,268,722	80,478,620
Common stock, shares outstanding		81,482,283	79,966,907
Common stock, shares unvested		17,188	25,000
Number of common stock shares repurchased		274,726	23,900
Repurchase of common stock		$ 11,223,000	$ 943,000
Quarterly cash dividend	$ 0.125	$ 0.125
Dividend declared period		2014-11
Dividend paid date		Dec. 15, 2014
Dividend record date		Dec. 01, 2014
Maximum [Member]
Class of Stock [Line Items]
Amount authorized for share repurchase program	$ 200,000,000
Class A Non-Voting Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares authorized		5,000,000	5,000,000
Common stock, shares issued		2,703,846	2,703,846
Common stock, shares outstanding		2,703,846	2,703,846
Quarterly cash dividend	$ 0.125