Stock-Based Compensation - Schedule of Information Regarding Standard and Market Condition Based Stock Options Outstanding (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Standard stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (in shares)	3,277,991	3,421,121	3,596,533	3,486,157
Options vested and expected to vest using estimated forfeiture rates (in shares)	3,175,002	3,223,919	3,452,487
Options exercisable (in shares)	2,633,990	2,131,268	2,252,744
Options outstanding, weighted average exercise price (in dollars per share)	$ 7.99	$ 8.44	$ 8.45	$ 8.30
Options vested and expected to vest using estimated forfeiture rates, Weighted Average Exercise Price (in dollars per share)	7.99	8.43	8.36
Options exercisable, Weighted Average Exercise Price (in dollars per share)	$ 7.94	$ 8.22	$ 7.59
Options outstanding, Weighted Average Remaining Contractual Life (years)	2 years 10 months 17 days	3 years 11 months 26 days	4 years 2 months 23 days
Options vested and expected to vest using estimated forfeiture rates, Weighted Average Remaining Contractual Life (years)	2 years 9 months 10 days	3 years 10 months 13 days	4 years 1 month 27 days
Options exercisable, Weighted Average Remaining Contractual Life (years)	2 years 1 month 20 days	3 years 1 month 6 days	3 years 6 months 21 days
Options outstanding, Aggregate Intrinsic Value	$ 2.2	$ 9.0	$ 12.5
Options vested and expected to vest using estimated forfeiture rates, Aggregate Intrinsic Value	2.2	8.5	12.3
Options exercisable, Aggregate Intrinsic Value	$ 2.1	$ 6.4	$ 9.9
Market condition based stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (in shares)	272,081	225,000	200,000	50,000
Options vested and expected to vest using estimated forfeiture rates (in shares)	272,081	209,141	184,125
Options exercisable (in shares)	272,081	65,625	0
Options outstanding, weighted average exercise price (in dollars per share)	$ 8.44	$ 8.39	$ 9.05	$ 11,940.00
Options vested and expected to vest using estimated forfeiture rates, Weighted Average Exercise Price (in dollars per share)	8.44	8.38	9.12
Options exercisable, Weighted Average Exercise Price (in dollars per share)	$ 8.44	$ 8.09	$ 0.00
Options outstanding, Weighted Average Remaining Contractual Life (years)	1 year 10 months 27 days	5 years 6 months	5 years 11 months 1 day
Options vested and expected to vest using estimated forfeiture rates, Weighted Average Remaining Contractual Life (years)	1 year 10 months 27 days	5 years 5 months 26 days	5 years 10 months 24 days
Options exercisable, Weighted Average Remaining Contractual Life (years)	1 year 10 months 27 days	5 years 2 months 1 day	0 days
Options outstanding, Aggregate Intrinsic Value	$ 0.0	$ 0.5	$ 0.5
Options vested and expected to vest using estimated forfeiture rates, Aggregate Intrinsic Value	0.0	0.5	0.5
Options exercisable, Aggregate Intrinsic Value	$ 0.0	$ 0.2	$ 0.0