Stock-based Compensation - Additional Information Regarding Options Outstanding (Detail)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Standard stock options | $3.72 - $3.72
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	$ 3.72
Exercise price range, upper range limit	$ 3.72
Number Outstanding (in shares) | shares	938
Weighted Average Remaining Contractual Life (Years)	1 year 6 months 14 days
Weighted Average Exercise Price (in dollars per share)	$ 3.72
Number Exercisable (in shares) | shares	938
Weighted Average Exercise Price (in dollars per share)	$ 3.72
Standard stock options | 3.85 - 3.85
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	3.85
Exercise price range, upper range limit	$ 3.85
Number Outstanding (in shares) | shares	600,000
Weighted Average Remaining Contractual Life (Years)	1 year 10 months 13 days
Weighted Average Exercise Price (in dollars per share)	$ 3.85
Number Exercisable (in shares) | shares	600,000
Weighted Average Exercise Price (in dollars per share)	$ 3.85
Standard stock options | 4.95 - 6.66
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	4.95
Exercise price range, upper range limit	$ 6.66
Number Outstanding (in shares) | shares	374,068
Weighted Average Remaining Contractual Life (Years)	4 years 1 month 17 days
Weighted Average Exercise Price (in dollars per share)	$ 6.34
Number Exercisable (in shares) | shares	263,312
Weighted Average Exercise Price (in dollars per share)	$ 6.23
Standard stock options | 6.86 - 8.09
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	6.86
Exercise price range, upper range limit	$ 8.09
Number Outstanding (in shares) | shares	405,525
Weighted Average Remaining Contractual Life (Years)	4 years 7 months 27 days
Weighted Average Exercise Price (in dollars per share)	$ 7.82
Number Exercisable (in shares) | shares	206,030
Weighted Average Exercise Price (in dollars per share)	$ 7.83
Standard stock options | 8.13 - 8.65
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	8.13
Exercise price range, upper range limit	$ 8.65
Number Outstanding (in shares) | shares	386,949
Weighted Average Remaining Contractual Life (Years)	4 years
Weighted Average Exercise Price (in dollars per share)	$ 8.54
Number Exercisable (in shares) | shares	196,434
Weighted Average Exercise Price (in dollars per share)	$ 8.56
Standard stock options | 8.70 - 9.19
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	8.70
Exercise price range, upper range limit	$ 9.19
Number Outstanding (in shares) | shares	378,506
Weighted Average Remaining Contractual Life (Years)	2 years 6 months 3 days
Weighted Average Exercise Price (in dollars per share)	$ 9.04
Number Exercisable (in shares) | shares	279,659
Weighted Average Exercise Price (in dollars per share)	$ 9.10
Standard stock options | 9.20 - 9.20
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	9.20
Exercise price range, upper range limit	$ 9.20
Number Outstanding (in shares) | shares	44,300
Weighted Average Remaining Contractual Life (Years)	6 months 14 days
Weighted Average Exercise Price (in dollars per share)	$ 9.20
Number Exercisable (in shares) | shares	44,300
Weighted Average Exercise Price (in dollars per share)	$ 9.20
Standard stock options | 9.53 - 9.53
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	9.53
Exercise price range, upper range limit	$ 9.53
Number Outstanding (in shares) | shares	734,000
Weighted Average Remaining Contractual Life (Years)	1 year 11 months 19 days
Weighted Average Exercise Price (in dollars per share)	$ 9.53
Number Exercisable (in shares) | shares	734,000
Weighted Average Exercise Price (in dollars per share)	$ 9.53
Standard stock options | 9.61 - 12.48
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	9.61
Exercise price range, upper range limit	$ 12.48
Number Outstanding (in shares) | shares	336,414
Weighted Average Remaining Contractual Life (Years)	2 years 7 months 20 days
Weighted Average Exercise Price (in dollars per share)	$ 11.82
Number Exercisable (in shares) | shares	292,026
Weighted Average Exercise Price (in dollars per share)	$ 11.92
Standard stock options | 12.49 - 14.02
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	12.49
Exercise price range, upper range limit	$ 14.02
Number Outstanding (in shares) | shares	17,291
Weighted Average Remaining Contractual Life (Years)	1 year 7 days
Weighted Average Exercise Price (in dollars per share)	$ 13.74
Number Exercisable (in shares) | shares	17,291
Weighted Average Exercise Price (in dollars per share)	$ 13.74
Standard stock options | $3.72 - $14.02
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	3.72
Exercise price range, upper range limit	$ 14.02
Number Outstanding (in shares) | shares	3,277,991
Weighted Average Remaining Contractual Life (Years)	2 years 10 months 17 days
Weighted Average Exercise Price (in dollars per share)	$ 7.99
Number Exercisable (in shares) | shares	2,633,990
Weighted Average Exercise Price (in dollars per share)	$ 7.94
Standard stock options | $8.09 - $8.09
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	8.09
Exercise price range, upper range limit	8.09
Standard stock options | 8.65 - 8.65
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	8.65
Exercise price range, upper range limit	$ 8.65
Market condition based stock options | $8.09 - $8.09
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number Outstanding (in shares) | shares	135,000
Weighted Average Remaining Contractual Life (Years)	1 year 10 months 27 days
Weighted Average Exercise Price (in dollars per share)	$ 8.09
Number Exercisable (in shares) | shares	135,000
Weighted Average Exercise Price (in dollars per share)	$ 8.09
Market condition based stock options | 8.65 - 8.65
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number Outstanding (in shares) | shares	84,581
Weighted Average Remaining Contractual Life (Years)	1 year 10 months 27 days
Weighted Average Exercise Price (in dollars per share)	$ 8.65
Number Exercisable (in shares) | shares	84,581
Weighted Average Exercise Price (in dollars per share)	$ 8.65
Market condition based stock options | 9.00 - 9.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	9.00
Exercise price range, upper range limit	$ 9.00
Number Outstanding (in shares) | shares	52,500
Weighted Average Remaining Contractual Life (Years)	1 year 10 months 27 days
Weighted Average Exercise Price (in dollars per share)	$ 9.00
Number Exercisable (in shares) | shares	52,500
Weighted Average Exercise Price (in dollars per share)	$ 9.00
Market condition based stock options | $8.09 - $9.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range, lower range limit	8.09
Exercise price range, upper range limit	$ 9.00
Number Outstanding (in shares) | shares	272,081
Weighted Average Remaining Contractual Life (Years)	1 year 10 months 27 days
Weighted Average Exercise Price (in dollars per share)	$ 8.44
Number Exercisable (in shares) | shares	272,081
Weighted Average Exercise Price (in dollars per share)	$ 8.44