Securities Sold Under Agreements to Repurchase - Maturity Schedule of Agreements (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Sep. 30, 2016
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	$ 142,741	$ 141,688
Municipal securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	2,475	0
Mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	140,266	141,688
Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	139,797	138,744
Overnight and Continuous | Municipal securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	2,475	0
Overnight and Continuous | Mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Total repurchase agreements	137,322	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	2,944	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	$ 2,944	$ 2,944