Shareholders' Equity (Details) - USD ($)		3 Months Ended	9 Months Ended
	Jul. 31, 2018	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Stock Repurchased [Abstract]
Issuance of common stock for contribution to non-qualified defined contribution retirement plans (in shares)			3,586	13,520
Per share price of shares issued (in dollars per share)			$ 715.00
Shares issued to individuals (in shares)				2,400
Total consideration for shares to be purchased		$ 31,152,000		$ 31,152,000
Estate of Former Director [Member]
Stock Repurchased [Abstract]
Per share price of shares issued (in dollars per share)	$ 700.00
Number of shares of stock purchased (in shares)	44,503
Total consideration for shares to be purchased	$ 31,152,100
Minimum [Member]
Stock Repurchased [Abstract]
Per share price of shares issued (in dollars per share)		$ 635.00		$ 635.00
Maximum [Member]
Stock Repurchased [Abstract]
Per share price of shares issued (in dollars per share)		$ 690.00		$ 690.00