Dividend (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended			6 Months Ended
	Apr. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Common stock dividend
Dividend declared (in dollars per share)	$ 0.22	$ 0.22		$ 0.22	$ 0.44	$ 0.44
Dividend paid (in dollars per share)		$ 0.22	$ 0.22	$ 0.22	$ 0.44	$ 0.44
Dividend paid (in dollars)		$ 2,763	$ 2,760		$ 5,523	$ 5,505
Dividend deferred in accordance with Deferred Compensation Plan		$ 18	$ 77