Stock Based Compensation and Stock Options - Stock Options Outstanding and Exercisable (Detail) - $ / shares	6 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Outstanding Options	1,135,586	1,167,042	1,163,179	1,136,073	1,118,530	1,115,984
Weighted Average Remaining Contractual Life	3 years 3 months 11 days
Outstanding Options - Weighted Average Exercise Price	$ 28.81	$ 28.15	$ 27.65	$ 26.42	$ 25.60	$ 24.80
Exercisable Options - Number of Exercisable Options	563,790
Exercisable Options - Weighted Average Exercise Price	$ 23.48
Range of Exercise Price, $9.05 to $23.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	9.05
Range of Exercise Price, upper limit	$ 23.00
Number of Outstanding Options	285,254
Weighted Average Remaining Contractual Life	3 years 3 months 18 days
Outstanding Options - Weighted Average Exercise Price	$ 17.66
Exercisable Options - Number of Exercisable Options	255,802
Exercisable Options - Weighted Average Exercise Price	$ 17.15
Range of Exercise Price, $23.01 to $24.64 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	23.01
Range of Exercise Price, upper limit	$ 24.64
Number of Outstanding Options	289,600
Weighted Average Remaining Contractual Life	2 years 3 months 4 days
Outstanding Options - Weighted Average Exercise Price	$ 23.56
Exercisable Options - Number of Exercisable Options	181,902
Exercisable Options - Weighted Average Exercise Price	$ 23.60
Range of Exercise Price, $24.65 to $34.78 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	24.65
Range of Exercise Price, upper limit	$ 34.78
Number of Outstanding Options	290,581
Weighted Average Remaining Contractual Life	3 years 10 months 21 days
Outstanding Options - Weighted Average Exercise Price	$ 33.19
Exercisable Options - Number of Exercisable Options	63,311
Exercisable Options - Weighted Average Exercise Price	$ 29.23
Range of Exercise Price, $34.79 to $45.55 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	34.79
Range of Exercise Price, upper limit	$ 45.55
Number of Outstanding Options	270,151
Weighted Average Remaining Contractual Life	3 years 8 months 16 days
Outstanding Options - Weighted Average Exercise Price	$ 41.51
Exercisable Options - Number of Exercisable Options	62,775
Exercisable Options - Weighted Average Exercise Price	$ 43.15