Benefit Plans (Details) - USD ($)	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures	737,267	5,334	32,700
Maximum contribution from employer	50.00%
Employer matching contribution, percent	6.00%
Amount of cost recognized	$ 1,512,752	$ 1,358,148	$ 1,377,371
Stock Option Plans
Number of shares available for grant (in shares)	206,541
Weighted-average fair value at the grant date	$ 53.50	$ 39.49	$ 22.25
Options Activity [Roll Forward]
Exercised (in shares)	(92,428)	(389,888)	(33,702)
Restricted Stock
Grant date fair value (in dollars per share)		$ 107.52	$ 51.15
Schedule of vesting of restricted shares on basis of compounded annual EPS growth [Abstract]
Compensation related to stock option and restricted stock plans	$ 17,635,309	$ 5,434,619	$ 4,810,698
Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Grant date fair value (in dollars per share)		$ 107.52	$ 51.15
Current Fiscal Year End Date	--03-31
Stock Options Plans [Member]
Stock Option Plans
Shares of authorized common stock reserved for issuance (in shares)	4,350,000
Options Activity [Roll Forward]
Options outstanding, beginning of year (in shares)	497,728
Granted (in shares)	324,870
Exercised (in shares)	(92,428)
Forfeited (in shares)	(8,330)
Expired (in shares)	(18,052)
Options outstanding, end of period (in shares)	703,788	497,728
Options exercisable, end of period (in shares)	299,661
Weighted Average Exercise Price [Roll Forward]
Options outstanding, beginning of year (in dollars per share)	$ 70.69
Granted (in dollars per share)	101.67
Exercised (in dollars per share)	64.89
Forfeited (in dollars per share)	77.66
Expired (in dollars per share)	82.92
Options outstanding, end of period (in dollars per share)	85.33	$ 70.69
Options exercisable, end of period (in dollars per share)	$ 70.72
Stock Option Activity Additional Disclosures
Weighted-average remaining contractual term, Options outstanding, end of period	7 years 2 months 5 days
Weighted-average remaining contractual terms, Options exercisable, end of period	4 years 6 months 18 days
Aggregate intrinsic value, Options outstanding, end of period	$ 22,391,720
Aggregate intrinsic value, Options exercisable, end of period	13,908,625
Intrinsic value of options exercised	4,433,495	$ 12,336,156	$ 661,164
Compensation Cost Not yet Recognized
Total unrecognized stock-based compensation expense related to non-vested stock options	$ 15,600,000
Weighted average period for recognition	5 years 2 months 1 day
Schedule of vesting of restricted shares on basis of compounded annual EPS growth [Abstract]
Compensation related to stock option and restricted stock plans	$ 3,991,967	$ 2,353,214	$ 3,490,662
Weighted average period for recognition	5 years 2 months 1 day
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	40,184
Stock Issued During Period, Shares, Share-based Compensation, Gross		24,456	74,490
Restricted Stock
Grant date fair value (in dollars per share)	$ 101.61
Schedule of vesting of restricted shares on basis of compounded annual EPS growth [Abstract]
Compensation related to stock option and restricted stock plans	$ 13,643,343	$ 3,081,405	$ 1,604,257
Summary of the status and changes in restricted stock [Roll Forward]
Outstanding at beginning of period (in shares)	73,810
Awards granted (in shares)	760,420
Outstanding at end of period (in shares)	783,450	73,810
Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Outstanding at beginning of period (in dollars per share)	$ 65.74
Grant date fair value (in dollars per share)	101.61
Vested during the period, net of cancellations (in dollars per share)	55.12
Cancelled during the period (in dollars per share)	98.47
Outstanding at end of period (in dollars per share)	$ 100.66	$ 65.74
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options	$ 65,900,000
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited	10,596
Equity Securities [Member]
Schedule of vesting of restricted shares on basis of compounded annual EPS growth [Abstract]
Compensation related to stock option and restricted stock plans	$ 17,635,310	$ 5,434,619
Equity Classified Awards [Member]
Schedule of vesting of restricted shares on basis of compounded annual EPS growth [Abstract]
Compensation related to stock option and restricted stock plans			5,094,919
Performance Shares [Member]
Compensation Cost Not yet Recognized
Weighted average period for recognition	4 years 6 months
Schedule of vesting of restricted shares on basis of compounded annual EPS growth [Abstract]
Weighted average period for recognition	4 years 6 months
Maximum [Member] | Stock Options Plans [Member]
Stock Option Plans
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years
Vesting period	5 years
Supplemental Employee Retirement Plans, Defined Benefit [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pension and Other Postretirement Benefits Cost (Reversal of Cost)	$ 648,971	750,669	618,013
Unfunded liability	$ 7,886,559	$ 8,258,550	$ 8,447,283
Annual salary increase used for estimating unfunded liability	3.50%	3.50%
Discount rate used for estimating unfunded liability	6.00%	6.00%
Retirement age used for estimating unfunded liability	65 years	65 years