Stockholders' Equity - Roll Forward of Class A Common Shares Outstanding (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Balance at the beginning of the year	52,095,166	55,711,325
Repurchases	(1,473,863)	(4,353,801)	(3,349,286)
Stock options, rights and ESPP issuances	246,625	593,574
Restricted share issuances	242,238	215,510
Restricted share forfeitures	(130,119)	(17,138)
Shares withheld for tax obligations	(71,780)	(54,304)
Balance at the end of the period	50,908,267	52,095,166	55,711,325