Reconciliation of Share Amount Used in Computation of Basic and Diluted Earnings Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Basic earnings per share-Weighted common shares outstanding	141,553	141,093	140,353
Weighted common shares assumed upon exercise of options and vesting of restricted stock units	1,965	957	768
Diluted earnings per share-Weighted common shares outstanding	143,518	142,050	141,121