Stockholders' Equity - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended			0 Months Ended
	Feb. 29, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 31, 2015	Jul. 31, 2013	Jan. 31, 2013	Dec. 27, 2012
Class of Stock [Line Items]
Common stock, shares authorized		110,000,000	110,000,000
Common stock entitles		One
Cost of non-voting common stock repurchased		$ 37,974,000		$ 75,133,000
Conversion of non voting common stock to voting common stock	763,924
Shares repurchase program authorized						65,000,000	35,000,000
Common stock shares repurchased		646,185
Cost of common stock shares repurchased		38,000,000
Shares repurchase program expiration date		Dec. 31, 2015
Special dividend paid								$ 1.30
Cash dividends declared per common share		$ 0.64	$ 0.52	$ 1.74
Quarterly dividends payable, date to be paid		Feb. 26, 2015
Quarterly dividends payable, date of record		Feb. 12, 2015
Subsequent Event [Member]
Class of Stock [Line Items]
Cash dividends declared per common share					$ 0.20
Common Stock Non-Voting [Member]
Class of Stock [Line Items]
Common stock, shares authorized		10,000,000	10,000,000
Non-voting common stock repurchased	1,821,730
Cost of non-voting common stock repurchased	52,900,000			$ 7,000
Common Stock Voting [Member]
Class of Stock [Line Items]
Common stock, shares authorized		110,000,000