Fair Value Measurements - Recurring (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Assets and liabilities measured at fair value on a recurring basis
Transfers of securities between levels	$ 0	$ 0
Assets:
Securities available-for-sale	568,227,000		$ 568,227,000		$ 531,838,000
Mortgage servicing rights	6,528,000		6,528,000		6,489,000
U.S. government agencies
Assets:
Securities available-for-sale					41,534,000
U.S. government agency mortgage-backed
Assets:
Securities available-for-sale	20,846,000		20,846,000
States and political subdivisions
Assets and liabilities measured at fair value on a recurring basis
Purchases			10,456,000
Assets:
Securities available-for-sale	225,518,000		225,518,000		68,703,000
Corporate bonds
Assets:
Securities available-for-sale	12,616,000		12,616,000		10,630,000
Collateralized mortgage obligations
Assets:
Securities available-for-sale	100,913,000		100,913,000		170,927,000
Asset-backed securities
Assets:
Securities available-for-sale	140,385,000		140,385,000		138,407,000
Collateralized loan obligations
Assets:
Securities available-for-sale	67,949,000		67,949,000		101,637,000
Level 2
Assets:
Securities available-for-sale	545,201,000		545,201,000		506,493,000
Loans held-for-sale	5,440,000		5,440,000		4,918,000
Liabilities:
Other liabilities	1,458,000		1,458,000		994,000
Level 3
Assets and liabilities measured at fair value on a recurring basis
Purchases				$ 0
Assets:
Securities available-for-sale	23,026,000		23,026,000		25,345,000
Recurring
Assets:
Total financial assets	580,899,000		580,899,000		544,205,000
Liabilities:
Total	1,843,000		1,843,000		1,667,000
Recurring | Finite-Lived Intangible Assets [Member]
Assets:
Loans held-for-sale	5,440,000		5,440,000		4,918,000
Mortgage servicing rights	6,528,000		6,528,000		6,489,000
Recurring | Interest rate swap agreements net of swap credit valuation
Liabilities:
Other liabilities	1,843,000		1,843,000		1,667,000
Recurring | Interest rate swap agreements net of swap credit valuation | Finite-Lived Intangible Assets [Member]
Assets:
Other assets	385,000		385,000		673,000
Recurring | Forward MBS contracts and forward loan contracts | Finite-Lived Intangible Assets [Member]
Assets:
Other assets	319,000		319,000		287,000
Recurring | U.S. government agency mortgage-backed | Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	20,846,000		20,846,000		41,534,000
Recurring | States and political subdivisions | Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	225,518,000		225,518,000		68,703,000
Recurring | Corporate bonds | Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	12,616,000		12,616,000		10,630,000
Recurring | Collateralized mortgage obligations | Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	100,913,000		100,913,000		170,927,000
Recurring | Asset-backed securities | Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	140,385,000		140,385,000		138,407,000
Recurring | Collateralized loan obligations | Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	67,949,000		67,949,000		101,637,000
Recurring | Level 2
Assets:
Total financial assets	551,345,000		551,345,000		512,371,000
Liabilities:
Total	1,843,000		1,843,000		1,667,000
Recurring | Level 2 | Finite-Lived Intangible Assets [Member]
Assets:
Loans held-for-sale	5,440,000		5,440,000		4,918,000
Recurring | Level 2 | Interest rate swap agreements net of swap credit valuation
Liabilities:
Other liabilities	1,843,000		1,843,000		1,667,000
Recurring | Level 2 | Interest rate swap agreements net of swap credit valuation | Finite-Lived Intangible Assets [Member]
Assets:
Other assets	385,000		385,000		673,000
Recurring | Level 2 | Forward MBS contracts and forward loan contracts | Finite-Lived Intangible Assets [Member]
Assets:
Other assets	319,000		319,000		287,000
Recurring | Level 2 | U.S. government agency mortgage-backed | Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	20,846,000		20,846,000		41,534,000
Recurring | Level 2 | States and political subdivisions | Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	205,170,000		205,170,000		46,477,000
Recurring | Level 2 | Corporate bonds | Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	12,616,000		12,616,000		10,630,000
Recurring | Level 2 | Collateralized mortgage obligations | Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	98,235,000		98,235,000		167,808,000
Recurring | Level 2 | Asset-backed securities | Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	140,385,000		140,385,000		138,407,000
Recurring | Level 2 | Collateralized loan obligations | Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	67,949,000		67,949,000		101,637,000
Recurring | Level 3
Assets:
Total financial assets	29,554,000		29,554,000		31,834,000
Recurring | Level 3 | Finite-Lived Intangible Assets [Member]
Assets:
Mortgage servicing rights	6,528,000		6,528,000		6,489,000
Recurring | Level 3 | States and political subdivisions | Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	20,348,000		20,348,000		22,226,000
Recurring | Level 3 | Collateralized mortgage obligations | Finite-Lived Intangible Assets [Member]
Assets:
Securities available-for-sale	$ 2,678,000		$ 2,678,000		$ 3,119,000