Stock-Based Compensation and Stock Options - Stock Options Outstanding and Exercisable (Detail) - $ / shares	9 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Outstanding Options	1,121,527	1,053,307	1,053,307	1,064,439	1,169,871	1,068,503	1,143,928
Weighted Average Remaining Contractual Life	3 years 6 months 10 days
Outstanding Options - Weighted Average Exercise Price	$ 44.08	$ 41.81	$ 41.81	$ 39.45	$ 38.41	$ 35.28	$ 32.02
Exercisable Options - Number of Exercisable Options	377,905
Exercisable Options - Weighted Average Exercise Price	$ 33.57
Range of Exercise Price, $12.71 to $32.10 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	12.71
Range of Exercise Price, upper limit	$ 32.10
Number of Outstanding Options	240,499
Weighted Average Remaining Contractual Life	2 years 5 months 23 days
Outstanding Options - Weighted Average Exercise Price	$ 25.78
Exercisable Options - Number of Exercisable Options	149,203
Exercisable Options - Weighted Average Exercise Price	$ 21.91
Range of Exercise Price, $32.11 to $43.32 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	32.11
Range of Exercise Price, upper limit	$ 43.32
Number of Outstanding Options	257,620
Weighted Average Remaining Contractual Life	2 years 10 months 20 days
Outstanding Options - Weighted Average Exercise Price	$ 37.51
Exercisable Options - Number of Exercisable Options	145,615
Exercisable Options - Weighted Average Exercise Price	$ 37.61
Range of Exercise Price, $43.33 to $49.40 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	43.33
Range of Exercise Price, upper limit	$ 49.40
Number of Outstanding Options	241,252
Weighted Average Remaining Contractual Life	3 years 7 months 28 days
Outstanding Options - Weighted Average Exercise Price	$ 47.37
Exercisable Options - Number of Exercisable Options	75,581
Exercisable Options - Weighted Average Exercise Price	$ 46.39
Range of Exercise Price, $49.41 to $59.32 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	49.41
Range of Exercise Price, upper limit	$ 59.32
Number of Outstanding Options	382,156
Weighted Average Remaining Contractual Life	4 years 7 months 9 days
Outstanding Options - Weighted Average Exercise Price	$ 58.23
Exercisable Options - Number of Exercisable Options	7,506
Exercisable Options - Weighted Average Exercise Price	$ 57.75