Schedule of Basic Weighted Average Shares Reconciles to Diluted Weighted Average Shares (Detail) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Basic weighted average common shares outstanding	82,482	82,402	82,820	81,994
Dilutive effect of stock options, unvested shares, and DCUs	888	1,184	965	1,539
Diluted weighted average common shares outstanding	83,370	83,586	83,785	83,533