Fair Value Measurements - Recurring (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Assets:
Securities available-for-sale	$ 541,439	$ 531,838
Mortgage servicing rights	6,944	6,489
U.S. Treasury
Assets:
Securities available-for-sale	3,947
U.S. government agencies
Assets:
Securities available-for-sale	13,061
U.S. government agency mortgage-backed
Assets:
Securities available-for-sale	12,214
States and political subdivisions
Assets and liabilities measured at fair value on a recurring basis
Purchases	16,712	14,296
Assets:
Securities available-for-sale	278,092	68,703
Corporate bonds
Assets:
Securities available-for-sale	833	10,630
Collateralized mortgage obligations
Assets:
Securities available-for-sale	65,939	170,927
Asset-backed securities
Assets:
Securities available-for-sale	112,932	138,407
Collateralized loan obligations
Assets:
Securities available-for-sale	54,421	101,637
Level 1
Assets:
Securities available-for-sale	3,947
Level 1 \| U.S. Treasury
Assets:
Securities available-for-sale	3,947
Level 2
Assets:
Securities available-for-sale	520,963	506,493
Loans held-for-sale	4,067	4,918
Liabilities:
Other liabilities	1,287
Level 2 \| Interest rate swap agreements net of swap credit valuation
Liabilities:
Other liabilities		994
Level 2 \| U.S. government agencies
Assets:
Securities available-for-sale	13,061
Level 2 \| U.S. government agency mortgage-backed
Assets:
Securities available-for-sale	12,214
Level 3
Assets:
Securities available-for-sale	16,529	25,345
Recurring
Assets:
Securities available-for-sale		41,534
Loans held-for-sale	4,067	4,918
Mortgage servicing rights	6,944	6,489
Total financial assets	553,415	544,205
Liabilities:
Total	2,014	1,667
Recurring \| Interest rate swap agreements net of swap credit valuation
Assets:
Other assets	727	673
Liabilities:
Other liabilities	2,014	1,667
Recurring \| Forward MBS contracts and forward loan contracts
Assets:
Other assets	238	287
Recurring \| States and political subdivisions
Assets:
Securities available-for-sale	278,092	68,703
Recurring \| Corporate bonds
Assets:
Securities available-for-sale	833	10,630
Recurring \| Collateralized mortgage obligations
Assets:
Securities available-for-sale	65,939	170,927
Recurring \| Asset-backed securities
Assets:
Securities available-for-sale	112,932	138,407
Recurring \| Collateralized loan obligations
Assets:
Securities available-for-sale	54,421	101,637
Recurring \| Level 1
Assets:
Total financial assets	3,947
Recurring \| Level 2
Assets:
Securities available-for-sale		41,534
Loans held-for-sale	4,067	4,918
Total financial assets	525,995	512,371
Liabilities:
Total	2,014	1,667
Recurring \| Level 2 \| Interest rate swap agreements net of swap credit valuation
Assets:
Other assets	727	673
Liabilities:
Other liabilities	2,014	1,667
Recurring \| Level 2 \| Forward MBS contracts and forward loan contracts
Assets:
Other assets	238	287
Recurring \| Level 2 \| States and political subdivisions
Assets:
Securities available-for-sale	263,831	46,477
Recurring \| Level 2 \| Corporate bonds
Assets:
Securities available-for-sale	833	10,630
Recurring \| Level 2 \| Collateralized mortgage obligations
Assets:
Securities available-for-sale	63,671	167,808
Recurring \| Level 2 \| Asset-backed securities
Assets:
Securities available-for-sale	112,932	138,407
Recurring \| Level 2 \| Collateralized loan obligations
Assets:
Securities available-for-sale	54,421	101,637
Recurring \| Level 3
Assets:
Mortgage servicing rights	6,944	6,489
Total financial assets	23,473	31,834
Recurring \| Level 3 \| States and political subdivisions
Assets:
Securities available-for-sale	14,261	22,226
Recurring \| Level 3 \| Collateralized mortgage obligations
Assets:
Securities available-for-sale	$ 2,268	$ 3,119

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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