Common Stock - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)
Schedule Of Common Stock [Line Items]
Senior leverage ratio	3.0
Share repurchase program, description	Under our credit facility, (described in Note 8, Debt and Financing Arrangements) share repurchases are unlimited when total leverage is less than 3.0. When leverage is greater than 3.0, the annual share repurchase is limited to $25 million
Cost of shares repurchased to settle statutory employee withholding related to vesting of stock awards	$ 19,735,000	$ 9,144,000	$ 36,482,000
Share Repurchase Program [Member]
Schedule Of Common Stock [Line Items]
Stock repurchase program authorized to be repurchased | shares	1,200,000	800,000
Payment for acquisition of treasury stock	$ 18,300,000	$ 7,800,000
Shares repurchased to settle statutory employee withholding related to vesting of stock awards | shares	100,000
Cost of shares repurchased to settle statutory employee withholding related to vesting of stock awards		$ 1,400,000
Maximum [Member]
Schedule Of Common Stock [Line Items]
Annual share repurchase limit	$ 25,000,000