Capital Structure (Detail)	12 Months Ended
	Dec. 31, 2018 USD ($) ClassOfCommonStock $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Feb. 28, 2017 USD ($)	Dec. 30, 2014 USD ($)
Equity, Class of Treasury Stock [Line Items]
Number of classes of common stock outstanding | ClassOfCommonStock	1
Acquisition of restricted stock from employees in connection with withholding tax payments (in shares) | shares	51,446	69,154	17,676
Withholding tax payments related to the vesting of restricted stock for total consideration	$ 3,122,000	$ 3,267,000	$ 807,000
Weighted average purchase price per share prior to the vesting date (in dollars per share) | $ / shares	$ 60.68	$ 47.24	$ 45.65
2014 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Repurchase of common stock authorized by board of directors up to					$ 20,000,000
Common stock shares purchased under the repurchase program (in shares) | shares		761,154
Common stock aggregate purchase price including commissions		$ 40,187,000
Common stock average purchase price per share (in dollars per share) | $ / shares		$ 52.80	$ 47.78
2014 Repurchase Program | Minimum
Equity, Class of Treasury Stock [Line Items]
Repurchase of common stock authorized by board of directors up to					$ 20,000,000
2017 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Additional authorized amount				$ 100,000,000
Authorized increase in repurchase amount, 2018				40,000,000
Authorized increase in repurchase amount, 2019				40,000,000
2017 Repurchase Program | Maximum
Equity, Class of Treasury Stock [Line Items]
Authorized increase in repurchase amount				$ 40,000,000
2014 and 2017 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Common stock shares purchased under the repurchase program (in shares) | shares	674,604		364,056
Common stock aggregate purchase price including commissions	$ 39,987,000		$ 17,396,000
Common stock average purchase price per share (in dollars per share) | $ / shares	$ 59.27