Stock-Based Compensation - Additional Information (Detail) - USD ($)					1 Months Ended	12 Months Ended
	Jul. 31, 2017	Jan. 31, 2017	Jul. 31, 2016	Jan. 31, 2016	May 30, 2009	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	May 30, 2017	May 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance					1,000,000
Grants in period, weighted average grant date fair value							$ 6.79	$ 6.04	$ 8.09
Intrinsic value of options exercised						$ 300,000	$ 100,000	$ 0
Shares
Options outstanding Beginning Balance						810,000	403,000
Options granted						419,000	472,000
Options exercised						(67,000)	(18,000)
Options forfeited						(56,000)	(47,000)
Options outstanding Ending Balance						1,106,000	810,000	403,000
Weighted Average Exercise Price
Options outstanding Beginning Balance						$ 15.72	$ 15.07
Options granted						17.55	16.20
Options exercised						15.28	13.33
Options forfeited						16.65	15.79
Options outstanding Ending Balance						$ 16.40	$ 15.72	$ 15.07
Number Outstanding as of December 31, 2017
Number Exercisable as of December 31, 2017						410,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term						5 years 7 months 21 days
Weighted Average Exercise Price (usd per share)						$ 15.37
Intrinsic value of stock options outstanding						$ 2,300,000
Intrinsic value of stock options exercisable						$ 1,300,000
Weighted Average Grant Date Fair Value (per share)
Shares of restricted stock repurchased to satisfy tax withholding obligations						198,043	162,101	193,088
Aggregate intrinsic value of restricted shares						$ 13,600,000
Total unrecognized compensation cost related to non-vested restricted shares						9,100,000
Compensation expense related to restricted shares						$ 5,900,000	$ 6,400,000	$ 5,100,000
Weighted Average Expected Option Phantom
Risk-free rate						2.49%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate						34.55%
Deferred Compensation Arrangement with Individual, Compensation Expense						$ 3,100,000
Tax benefit attributable to all recorded stock-based compensation							$ 2,600,000	$ 2,400,000
$12.97
Number Outstanding as of December 31, 2017
Number Outstanding as of December 31, 2017						1,106,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term						7 years 6 months 22 days
Weighed Average Exercise Price (usd per share)						$ 16.40
Stock Incentive 1999 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance					4,829,344
Stock Options And Employee Stock Purchase Plan
Weighted Average Grant Date Fair Value (per share)
Granted (usd per share)							$ 3.48	$ 3.01	$ 3.13
Fair value of equity instrument other than options							$ 176,000		$ 139,000
Weighted Average Expected Option Phantom
Compensation expense related to options and ESPP rights						$ 175,575
Cash received from exercise of options and ESPP						$ 1,800,000	$ 900,000	$ 500,000
Shares under the Amended and Restated 2009 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance					600,000						2,700,000
Shares available for future grants						243,656
Weighted Average Grant Date Fair Value (per share)
Total unrecognized compensation cost, weighted-average recognition period						1 year
Percentage of compensation that participating employees can contribute to purchase common stock, minimum					1.00%
Percentage of compensation that participating employees can contribute to purchase common stock, maximum					15.00%
Common shares that participating employees can purchase in any plan year, shares					1,000
Percentage of discount from fair market value that eligible employees can purchase common stock					15.00%
Common shares that participating employees can purchase in any plan year, amount					$ 25,000
Shares issued under the ESPP	26,130	24,379	24,529	29,480		50,000	54,000
Shares issued under ESPP, weighted average price (usd per share)	$ 15.54	$ 16.01	$ 12.77	$ 12.61
Weighted Average Expected Option Phantom
Expected term						6 months	6 months	6 months
Risk-free rate, minimum						0.65%	0.40%
Risk-free rate, maximum						1.15%	0.47%
Risk-free rate								0.05%
Expected volatility, minimum						10.30%	14.00%	17.40%
Expected volatility, maximum						12.60%	19.20%	23.80%
Dividend Yield						0.00%	0.00%	0.00%
Intrinsic value of ESPP						$ 72,000
Intrinsic value of ESPP shares purchased						158,000
Unrecognized compensation cost related to non-vested stock options						$ 15,000
Shares under the 2017 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance										3,700,000
Shares available for future grants						4,966,712
Shares under the 2017 Stock Incentive Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, terms					10 years
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense							$ 1,700,000	$ 1,200,000	$ 500,000
Weighted Average Expected Option Phantom
Expected term						6 years 3 months	6 years 3 months
Risk-free rate, minimum							1.54%	2.10%
Risk-free rate, maximum							1.91%	2.30%
Expected volatility, minimum							35.00%	38.30%
Expected volatility, maximum							36.30%	47.30%
Dividend Yield						0.00%	0.00%	0.00%
Stock options | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards, vesting period					4 years
Weighted Average Expected Option Phantom
Expected term								7 years
Stock options | Minimum
Weighted Average Expected Option Phantom
Expected term								6 years 3 months
Performance based restricted stock
Restricted Stock
Granted (shares)						0
Weighted Average Grant Date Fair Value (per share)
Remaining expense on non-vested shares outstanding							$ 0
Shares paid for tax withholding						11,803	12,954	12,882
Performance based restricted stock | Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation expense							$ 600,000	$ 400,000
Restricted Stock
Granted (shares)							31,250	31,250
Restricted stock
Restricted Stock
Unvested, Beginning Balance (shares)						980,000	1,014,000
Granted (shares)						422,000	559,000
Vested (shares)						(509,000)	(429,000)
Forfeited (shares)						(157,000)	(164,000)
Unvested, Ending Balance (shares)						736,000	980,000	1,014,000
Weighted Average Grant Date Fair Value (per share)
Unvested, Beginning Balance (usd per share)						$ 15.05	$ 13.11
Granted (usd per share)						17.77	16.49	$ 16.30
Vested (usd per share)						14.13	12.76
Forfeited (usd per share)						15.99	14.06
Unvested, Ending Balance (usd per share)						$ 17.04	$ 15.05	$ 13.11
Fair value of equity instrument other than options						$ 9,100,000	$ 5,500,000	$ 5,200,000
Total unrecognized compensation cost, weighted-average recognition period						2 years 3 months 7 days
Restricted stock | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards, vesting period					4 years
Restricted stock | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards, vesting period					1 year