Treasury Stock (Detail) - USD ($)	12 Months Ended			123 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 28, 2018
Subsequent Event [Line Items]
Common stock amount authorized under repurchase program, value	$ 150,000,000.0	$ 189,800,000
Addition to authorized amount		$ 39,800,000
Repurchase of common stock (in shares)		2,175,268	5,598,094
Payment for repurchase of common stock, net of fees		$ 30,400,000
Average stock price of shares repurchased (in dollars per share)		$ 13.95	$ 13.17
Payments for treasury stock	$ 30,434,000	$ 74,265,000	$ 1,702,000
Subsequent Event
Subsequent Event [Line Items]
Remaining authorized repurchase amount				$ 30,500,000
Repurchase of common stock (in shares)				13,761,211
Average stock price of shares repurchased (in dollars per share)				$ 11.58
Payments for treasury stock				$ 159,300,000