Stock-Based Compensation - Schedule of Information Regarding Standard and Market Condition Based Stock Options Outstanding (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Standard Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding, Number of Shares	3,675,153	3,486,157	3,227,167
Options vested and expected to vest using estimated forfeiture rates, Number of Shares	3,529,945	3,319,308
Options exercisable, Number of Shares	2,270,159	2,023,024
Options outstanding, Weighted Average Exercise Price	$ 8.21	$ 8.30
Options vested and expected to vest using estimated forfeiture rates, Weighted Average Exercise Price	$ 8.16	$ 8.21
Options exercisable, Weighted Average Exercise Price	$ 7.50	$ 7.18
Options outstanding, Weighted Average Remaining Contractual Life (years)	4 years 8 months 5 days	4 years 10 months 6 days
Options vested and expected to vest using estimated forfeiture rates, Weighted Average Remaining Contractual Life (years)	4 years 7 months 13 days	4 years 9 months 18 days
Options exercisable, Weighted Average Remaining Contractual Life (years)	4 years 7 days	4 years 3 months 4 days
Options outstanding, Aggregate Intrinsic Value	$ 6.3	$ 6.6
Options vested and expected to vest using estimated forfeiture rates, Aggregate Intrinsic Value	6.2	6.6
Options exercisable, Aggregate Intrinsic Value	5.6	6.0
Market Condition Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding, Number of Shares	200,000	50,000	0
Options vested and expected to vest using estimated forfeiture rates, Number of Shares	130,330	45,430
Options exercisable, Number of Shares	0	0
Options outstanding, Weighted Average Exercise Price	$ 9.05	$ 11.94
Options vested and expected to vest using estimated forfeiture rates, Weighted Average Exercise Price	$ 9.26	$ 11.94
Options exercisable, Weighted Average Exercise Price	$ 0.00	$ 0.00
Options outstanding, Weighted Average Remaining Contractual Life (years)	6 years 8 months 1 day	6 years 1 month 24 days
Options vested and expected to vest using estimated forfeiture rates, Weighted Average Remaining Contractual Life (years)	6 years 7 months 10 days	6 years 1 month 24 days
Options exercisable, Weighted Average Remaining Contractual Life (years)	0 years	0 years
Options outstanding, Aggregate Intrinsic Value	0.2	0
Options vested and expected to vest using estimated forfeiture rates, Aggregate Intrinsic Value	0.1	0
Options exercisable, Aggregate Intrinsic Value	$ 0	$ 0