Securities Sold Under Agreements to Repurchase - Maturity Schedule of Agreements (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Sep. 30, 2016
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	$ 123,851	$ 141,688
Municipal securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	3,673	0
Mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	120,178	141,688
Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	123,851	138,744
Overnight and Continuous | Municipal securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	3,673	0
Overnight and Continuous | Mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	120,178	138,744
Up to 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	0	0
Up to 30 Days | Municipal securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	0	0
Up to 30 Days | Mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	0	0
30-90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	0	0
30-90 Days | Municipal securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	0	0
30-90 Days | Mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	0	0
Greater than 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	0	2,944
Greater than 90 Days | Municipal securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	0	0
Greater than 90 Days | Mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	$ 0	$ 2,944