Stock-based Compensation - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Aug. 31, 2006	Apr. 30, 2008	Feb. 28, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Tax benefit from compensation expense	$ 3.8	$ 2.7	$ 1.9
Cash received from exercise of stock options	24.1	27.8	14.4
Cash received associated with tax benefit	18.8	31.8	6.5
Intrinsic value of options exercised	56.1	87.8	17.6
2006 Plan [Member] | Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized under equity-based incentive plan				11,173,819
Equity based incentive plan expiry period from date of grant	10 years
Equity-based incentive plan, description	Under the 2006 Plan, the exercise price of awards is set on the grant date and may not be less than the fair market value per share on such date.
2008 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Initial authorized shares					1,416,661
2008 Plan [Member] | Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized under equity-based incentive plan					9,498,306
Equity based incentive plan expiry period from date of grant	10 years
Equity-based incentive plan, description	There is an annual increase to be added on the first day of each of the Company’s fiscal years during the term of the 2008 stock incentive plan beginning in fiscal 2009 equal to the lesser of (i) 1,416,661 shares of common stock, (ii) 2% of the outstanding shares on such date or (iii) an amount determined by the Company’s board of directors. Under the 2008 Plan, which became effective in July 2008, the exercise price of awards is set on the grant date and may not be less than the fair market value per share on such date. Generally, awards expire ten years from the date of grant. The Company has granted time-based options under the 2008 Plan.
Percentage increase in share of outstanding share	2.00%
2014 Plan [Member] | Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized under equity-based incentive plan						3,000,000
Equity based incentive plan expiry period from date of grant	10 years
Time-Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based incentive plan, description	Time-based options granted under the 2006 Plan, the 2008 Plan or the 2014 Plan generally vest 25% on the first anniversary of the grant date and 1/36th of the remaining balance each month thereafter for 36 months. All outstanding time-based options vest upon a change in control, subject to certain conditions.
Performance based option vesting period	36 months
Equity based incentive plan percentage of first anniversary	25.00%
Remaining balance percentage of equity based incentive plan period	0.02778%
Time based options granted weighted average granted fair value	$ 12.77	$ 9.86	$ 5.79
Share-based payment award, options, vested in period, fair value	11.3	8.2	4.9
Stock based compensation related to time based options	$ 48.2
Employee service share-based compensation period for recognition of expense	3 years
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee service share-based compensation period for recognition of expense	32 months	44 months	3 months
Restricted Stock [Member] | 2006 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted shares, granted	25,000
Equity based incentive plan percentage of first anniversary	25.00%
Remaining balance percentage of equity based incentive plan period	0.08333%
Restricted Stock [Member] | 2006 Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance based option vesting period	3 years