Income Taxes - Unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Net changes in the liability for unrecognized tax benefits
Balance at the beginning of the period	$ 13,248	$ 16,932
Additions (reductions) for tax positions taken in prior years		399
Reductions for tax positions taken in prior years	(80)
Recognition of benefits from expiration of statutes	(1,770)	(26)
Recognition of benefits from open years effectively settled		(5,359)
Additions for tax positions related to the current year	713	1,302
Additions (reductions) for tax positions related to current year acquisitions	(2,169)
Balance at the end of the period	9,942	13,248	$ 16,932
Unrecognized tax benefits from permanent tax adjustments that, if recognized, would affect the effective rate	1,800	3,700
Unrecognized tax benefits related to settlements with taxing authorities	1,100
Cash amounts paid for income taxes, net of refunds received	$ 15,700	$ 1,600	$ 14,200