Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 1,074,313
Other comprehensive income, net of tax	19,239	$ 20,110
Net Change		19,622
Balance at end of period	1,108,728	1,029,999
Effect of adoption of the stranded tax effect account standard
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Foreign currency translation adjustment	0
Income tax benefit	0
Other comprehensive income, net of tax	0
Effect of the adoption of the stranded tax effect accounting standard		(497)
Income tax benefit		9
Effect of the adoption of the stranded tax effect accounting standard, net of tax		(488)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(14,104)	(23,238)
Balance at end of period	5,135	(3,616)
Accumulated foreign currency adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Foreign currency translation adjustment	21,543	15,819
Income tax benefit	82	32
Other comprehensive income, net of tax	21,625	15,851
Interest rate swap contract
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Income tax benefit	689	(1,225)
Other comprehensive income, net of tax	(2,386)	4,259
Change in fair value	(6,449)	4,314
Reclassification adjustment into earnings	$ 3,374	$ 1,170