Stock Repurchase Program (Detail) - USD ($) shares in Thousands	9 Months Ended
	Sep. 30, 2018	Feb. 28, 2018	Nov. 01, 2015
Equity, Class of Treasury Stock [Line Items]
Stock repurchased during period, value	$ 142,262,000
Repurchase Program April 2017
Equity, Class of Treasury Stock [Line Items]
Authorized common stock to be repurchased			$ 100,000,000
Stock Repurchase Program, Aggregate Number of Shares Repurchased	1,744
Shares repurchased, value	$ 100,000,000
Repurchase of common stock (in shares)	803
Stock repurchased during period, value	$ 45,200,000
Repurchase Program February 2018
Equity, Class of Treasury Stock [Line Items]
Authorized common stock to be repurchased		$ 150,000,000
Repurchase of common stock (in shares)	1,947
Stock repurchased during period, value	$ 97,062,000
Stock repurchase program, remaining authorized repurchase amount	52,938,000
Repurchase Program April 2017 and February 2018
Equity, Class of Treasury Stock [Line Items]
Stock repurchased during period, value	$ 142,262,000