Schedule of Basic Weighted Average Shares Reconciles to Diluted Weighted Average Shares Outstanding (Detail) - shares shares in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Basic weighted average common shares outstanding	76,211	76,831	77,466	77,996	78,669	79,558	80,106	80,527	77,126	79,715	81,517
Dilutive effect of stock options, restricted stock, performance share units and DCUs									846	1,013	972
Diluted weighted average common shares outstanding	77,091	77,646	78,297	78,856	79,632	80,561	81,149	81,575	77,972	80,728	82,489