Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 15, 2017
Equity [Line Items]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.07
Dividends	$ 9,896
Stock Repurchase Program, Authorized Amount				$ 100,000
Payments for Repurchase of Common Stock	$ 28,000	$ 7,573	$ 0
Shares absorbed into plan			5,700
Term of plan, in years	10 years
Weighted average remaining contractual term option outstanding	4 years 1 month
Weighted average remaining contractual term option exercisable	2 years 11 months
Shares available for future grants	8,800	9,400	10,400
Total pre-tax intrinsic value of stock options exercised	$ 4,800	$ 5,100
Total pre-tax intrinsic value based on the closing stock price	$ 30.45
Intrinsic value of stock options outstanding	$ 31,800
Intrinsic value of stock options exercisable	$ 16,900
Weighted average remaining contractual term for unvested restricted shares, in years	2 years 1 month	2 years 5 months
performance shares granted	100	200	200
Share-based payment awards in the form of stock option awards	335	549	411
Contractual term of stock options (in years)	7 years
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	2 years 6 months
Minimum
Equity [Line Items]
Vesting period, in years	3 years
Maximum
Equity [Line Items]
Vesting period, in years	4 years
Unvested Stock Options
Equity [Line Items]
Total compensation cost not yet recognized	$ 2,600
Restricted Stock
Equity [Line Items]
Total compensation cost not yet recognized	$ 21,100
Employee Stock Purchase Plan
Equity [Line Items]
Shares available for future grants	2,100
Percentage of employee contribution from compensation	10.00%
Rate of discount from the fair market value	15.00%
Shares purchase by employees	200	300	300
Weighted-average price per share paid by the employees	$ 16.92	$ 11.56	$ 11.21