Borrowings (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets Sold under Agreements to Repurchase [Line Items]
Fair value of collateral	$ 7,000	$ 68,100	$ 18,800
Federal Home Loan Bank of Topeka [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Federal Home Loan Bank, Advances, General Debt Obligations, Maximum Amount Available	$ 903,900
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Interest Rate	0.72%
FHLB advances	$ 13,700	0	0
Federal Home Loan Bank of Des Moines [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Fair value of collateral	28,800	41,700	0
FHLB advances	25,000	25,000	25,000
Interest expense related to FHLB advances	$ 693	$ 666	$ 164
Federal Home Loan Bank of Des Moines [Member] | Minimum
Assets Sold under Agreements to Repurchase [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Interest Rate	1.81%
Federal Home Loan Bank of Des Moines [Member] | Maximum
Assets Sold under Agreements to Repurchase [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Interest Rate	2.33%
Maturity Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Average interest rate	0.17%	0.18%	0.13%
Maturity on Demand [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Amount of repurchase agreements	$ 0	$ 0	$ 0
U.S. Treasury Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Fair value of collateral	$ 99,100	$ 205,700	$ 152,400