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Fair Value Measurements - Recurring (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Assets:
Securities available-for-sale	$ 543,644	$ 543,644	$ 541,439
Mortgage servicing rights	7,812		6,944
U.S. Treasury
Assets:
Securities available-for-sale	3,876		3,947
U.S. government agencies
Assets:
Securities available-for-sale	12,216		13,061
U.S. government agency mortgage-backed
Assets:
Securities available-for-sale	13,407
States and political subdivisions
Assets and liabilities measured at fair value on a recurring basis
Purchases	19,934	$ 10,456
Assets:
Securities available-for-sale	276,112		278,092
Corporate bonds
Assets:
Securities available-for-sale	700		833
Collateralized mortgage obligations
Assets:
Securities available-for-sale	61,432		65,939
Asset-backed securities
Assets:
Securities available-for-sale	109,263		112,932
Collateralized loan obligations
Assets:
Securities available-for-sale	66,638		54,421
Level 1
Assets:
Securities available-for-sale	3,876		3,947
Level 2
Assets:
Securities available-for-sale	519,548		520,963
Loans held-for-sale	5,206		4,067
Liabilities:
Other liabilities			1,287
Level 3
Assets:
Securities available-for-sale	20,220		16,529
Recurring
Assets:
Securities available-for-sale			13,061
Total financial assets	559,210		553,415
Liabilities:
Total	2,287		2,014
Recurring \| Finite-Lived Intangible Assets [Member]
Assets:
Loans held-for-sale	5,206		4,067
Mortgage servicing rights	7,812		6,944
Recurring \| Interest rate swap agreements net of swap credit valuation
Liabilities:
Other liabilities	2,287		2,014
Recurring \| Interest rate swap agreements net of swap credit valuation \| Finite-Lived Intangible Assets [Member]
Assets:
Other assets	2,287		727
Recurring \| Forward MBS contracts and forward loan contracts \| Finite-Lived Intangible Assets [Member]
Assets:
Other assets	261		238
Recurring \| U.S. Treasury
Assets:
Securities available-for-sale			3,947
Recurring \| U.S. Treasury \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	3,876
Recurring \| U.S. government agencies \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	12,216
Recurring \| U.S. government agency mortgage-backed \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	13,407		12,214
Recurring \| States and political subdivisions \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	276,112		278,092
Recurring \| Corporate bonds \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	700		833
Recurring \| Collateralized mortgage obligations \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	61,432		65,939
Recurring \| Asset-backed securities \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	109,263		112,932
Recurring \| Collateralized loan obligations \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	66,638		54,421
Recurring \| Level 1
Assets:
Total financial assets	3,876		3,947
Recurring \| Level 1 \| U.S. Treasury
Assets:
Securities available-for-sale			3,947
Recurring \| Level 1 \| U.S. Treasury \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	3,876
Recurring \| Level 2
Assets:
Securities available-for-sale			13,061
Total financial assets	527,302		525,995
Liabilities:
Total	2,287		2,014
Recurring \| Level 2 \| Finite-Lived Intangible Assets [Member]
Assets:
Loans held-for-sale	5,206		4,067
Recurring \| Level 2 \| Interest rate swap agreements net of swap credit valuation
Liabilities:
Other liabilities	2,287		2,014
Recurring \| Level 2 \| Interest rate swap agreements net of swap credit valuation \| Finite-Lived Intangible Assets [Member]
Assets:
Other assets	2,287		727
Recurring \| Level 2 \| Forward MBS contracts and forward loan contracts \| Finite-Lived Intangible Assets [Member]
Assets:
Other assets	261		238
Recurring \| Level 2 \| U.S. government agencies \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	12,216
Recurring \| Level 2 \| U.S. government agency mortgage-backed \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	13,407		12,214
Recurring \| Level 2 \| States and political subdivisions \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	257,663		263,831
Recurring \| Level 2 \| Corporate bonds \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	700		833
Recurring \| Level 2 \| Collateralized mortgage obligations \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	59,661		63,671
Recurring \| Level 2 \| Asset-backed securities \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	109,263		112,932
Recurring \| Level 2 \| Collateralized loan obligations \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	66,638		54,421
Recurring \| Level 3
Assets:
Total financial assets	28,032		23,473
Recurring \| Level 3 \| Finite-Lived Intangible Assets [Member]
Assets:
Mortgage servicing rights	7,812		6,944
Recurring \| Level 3 \| States and political subdivisions \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	18,449		14,261
Recurring \| Level 3 \| Collateralized mortgage obligations \| Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	$ 1,771		$ 2,268