Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		$ (14,899)			$ (14,899)
Other comprehensive income (loss)	$ (12,051)	4,972	$ (3,539)	$ (6,217)
Ending balance	(21,978)				(21,978)
Unrealized Gains (Losses) on AFS Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	9,698	10,150	537	(2,990)	10,150	$ (2,990)
Other comprehensive income (loss), before reclassifications	10,378		3,061		9,926	6,588
Amount reclassified from AOCI	0		0		0	0
Other comprehensive income (loss)	10,378		3,061		9,926	6,588
Ending balance	20,076	9,698	3,598	537	20,076	3,598
Unrealized Gains (Losses) on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(19,625)	(25,049)	(2,414)	7,330	(25,049)	7,330
Other comprehensive income (loss), before reclassifications	(23,412)		(6,500)		(18,697)	(16,395)
Amount reclassified from AOCI	983		(100)		1,692	51
Other comprehensive income (loss)	(22,429)		(6,600)		(17,005)	(16,344)
Ending balance	(42,054)	(19,625)	(9,014)	(2,414)	(42,054)	(9,014)
AOCI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(9,927)	(14,899)	(1,877)	4,340	(14,899)	4,340
Other comprehensive income (loss), before reclassifications	(13,034)		(3,439)		(8,771)	(9,807)
Amount reclassified from AOCI	983		(100)		1,692	51
Other comprehensive income (loss)	(12,051)	4,972	(3,539)	(6,217)	(7,079)	(9,756)
Ending balance	$ (21,978)	$ (9,927)	$ (5,416)	$ (1,877)	$ (21,978)	$ (5,416)