Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Reversal amount of tax benefit as a result of change in the regulations	$ 2,500
Current:
Federal		$ 22,282	$ 59,855	$ 68,608
Foreign		6,120	10,132	11,039
State		4,730	15,339	11,344
Total current portion		33,132	85,326	90,991
Deferred:
Federal		10,177	4,905	(26,001)
Foreign		1,321	(1,498)	1,868
State		2,092	1,808	3,522
Total deferred portion		13,590	5,215	(20,611)
Total provision for income taxes		$ 46,722	$ 90,541	$ 70,380