Shareholders' Equity - Summary of Activity Related to Shares of Common Stock Issued and Repurchased (Detail)	3 Months Ended
	Mar. 31, 2018 shares
Common Stock Outstanding [Line Items]
Beginning balance	90,104,885
Common stock issued and exercise of stock options	409,794
Shares withheld for tax withholding and exercises	(162,846)
Shares repurchased under stock repurchase programs	(492,175)
Ending balance	89,859,658
Common Stock Issued [Member]
Common Stock Outstanding [Line Items]
Beginning balance	129,543,856
Dividend payable/paid	111
Common stock issued and exercise of stock options	409,794
Ending balance	129,953,761
Treasury Stock [Member]
Common Stock Outstanding [Line Items]
Beginning balance	(39,438,971)
Dividend payable/paid	(111)
Shares withheld for tax withholding and exercises	(162,846)
Shares repurchased under stock repurchase programs	(492,175)
Ending balance	(40,094,103)