Share-Based Compensation Plans - Additional Information (Detail) $ / shares in Units, $ in Millions		1 Months Ended		3 Months Ended				9 Months Ended
	Apr. 15, 2015 shares	Jul. 31, 2015 $ / shares shares	Jul. 31, 2014 $ / shares shares	Sep. 30, 2015 USD ($) shares	Mar. 31, 2015	Sep. 30, 2014 USD ($)	Mar. 31, 2014	Sep. 30, 2015 USD ($) CompensationPlan shares	Sep. 30, 2014 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employee stock purchase programs | CompensationPlan								2
Share-based payment arrangements | $				$ 17.0		$ 16.3		$ 61.1	$ 53.0
Unrecognized compensation expenses related to share-based payment arrangements | $				$ 95.2				$ 95.2
Weighted-average period of recognizing unrecognized compensation expenses related to share-based compensation, in years								2 years
2012 Long Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized	1,500,000
Number of remaining shares that may be issued				6,377,456				6,377,456
Directors Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of remaining shares that may be issued				31,462				31,462
Management Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value assumptions, risk-free interest rate		0.16%	0.07%
Fair value assumptions, dividend yield		0.60%	0.60%
Fair value assumptions, expected life in years		7 months 6 days	7 months 6 days
Expected number of shares to be purchased in the period		200,000
Number of shares purchased in period			200,000
Fair value per share of shares authorized for issuance | $ / shares		$ 60.47	$ 51.82
Fair value assumptions, expected volatility		17.00%	20.00%
Performance Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award requisite service periods					3 years		3 years
Share-based Compensation Arrangement by Share-based Payment Award, Terms of Award								These units have requisite service periods of three years and have no dividend rights.
Fair value assumptions, risk-free interest rate					0.86%		0.70%
Fair value assumptions, dividend yield					0.51%		0.62%
Fair value assumptions, expected life in years					2 years 9 months 11 days		2 years 10 months 17 days