Stock-Based Compensation - Schedule of Information Regarding Standard and Market Condition Based Stock Options Outstanding (Detail) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014	Dec. 31, 2013
Standard Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding, number of shares	3,612,753	3,486,157	3,227,167
Options vested and expected to vest using estimated forfeiture rates, number of shares	3,460,999	3,319,308
Options exercisable, number of shares	2,203,208	2,023,024
Options outstanding, Weighted Average Exercise Price (in dollars per share)	$ 8.27	$ 8.30
Options vested and expected to vest using estimated forfeiture rates, Weighted Average Exercise Price (in dollars per share)	8.21	8.21
Options exercisable, Weighted Average Exercise Price (in dollars per share)	$ 7.47	$ 7.18
Options outstanding, Weighted Average Remaining Contractual Life (years)	4 years 6 months 10 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 5 months 15 days	4 years 9 months 18 days
Options exercisable, Weighted Average Remaining Contractual Life (years)	3 years 9 months 18 days	4 years 3 months 4 days
Options outstanding, aggregate intrinsic value	$ 16.5	$ 6.6
Options vested and expected to vest using estimated forfeiture rates, Aggregate Intrinsic Value	16.0	6.6
Options exercisable, aggregate intrinsic value	$ 12.0	$ 6.0
Market Condition Based Stock Options
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	176,570	45,430
Options exercisable, number of shares	0	0
Options outstanding, Weighted Average Exercise Price (in dollars per share)	$ 9.05	$ 11.94
Options vested and expected to vest using estimated forfeiture rates, Weighted Average Exercise Price (in dollars per share)	9.12	11.94
Options exercisable, Weighted Average Exercise Price (in dollars per share)	$ 0.00	$ 0.00
Options outstanding, Weighted Average Remaining Contractual Life (years)	6 years 5 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 4 months 24 days	6 years 1 month 24 days
Options exercisable, Weighted Average Remaining Contractual Life (years)
Options outstanding, aggregate intrinsic value	$ 0.7	$ 0.0
Options vested and expected to vest using estimated forfeiture rates, Aggregate Intrinsic Value	0.6	0.0
Options exercisable, aggregate intrinsic value	$ 0.0	$ 0.0