Shareholders' Equity - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2011 Vote	Dec. 31, 2010	Dec. 31, 2009
Stockholders Equity Note [Line Items]
Common stock, share repurchase	6,000,000	2,000,000
Voting rights, description	are generally entitled to one vote per share until they have been held by the same beneficial owner for a continuous period of 48 months, at which time they become entitled to 10 votes per share
Voting rights, votes per share	1
Share Held For Continuous Forty Eight Month Period
Stockholders Equity Note [Line Items]
Voting rights, votes per share	10
Share Repurchase Authorization 2008
Stockholders Equity Note [Line Items]
Remaining common stock available for purchase under share repurchase authorizations	24,400,000