Fair Value Measurements (Details 2) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets:
Investment securities, available-for-sale	$ 942,076	$ 904,033
Mortgages held for sale	8,626	13,123
U.S. Treasury and Federal agencies securities
Assets:
Investment securities, available-for-sale	502,997	468,119
U.S. States and political subdivisions securities
Assets:
Investment securities, available-for-sale	97,985	116,000
Mortgage-backed securities - Federal agencies
Assets:
Investment securities, available-for-sale	296,330	287,910
Corporate debt securities
Assets:
Investment securities, available-for-sale	44,056	31,294
Foreign government and other securities
Assets:
Investment securities, available-for-sale	708	710
Total
Assets:
Investment securities, available-for-sale	942,076	904,033
Mortgages held for sale	8,626	13,123
Level 1
Assets:
Investment securities, available-for-sale	27,726	27,971
Mortgages held for sale	0	0
Level 2
Assets:
Investment securities, available-for-sale	911,487	873,197
Mortgages held for sale	8,626	13,123
Level 3
Assets:
Investment securities, available-for-sale	2,863	2,865
Mortgages held for sale	0	0
Recurring basis | Total
Assets:
Investment securities, available-for-sale	942,076	904,033
Mortgages held for sale	8,626	13,123
Total	956,044	922,323
Liabilities:
Total	5,439	5,262
Recurring basis | Total | Interest rate swap contracts
Assets:
Accrued income and other assets	5,342	5,167
Liabilities:
Accrued expenses and other liabilities	5,439	5,262
Recurring basis | Total | U.S. Treasury and Federal agencies securities
Assets:
Investment securities, available-for-sale	502,997	468,119
Recurring basis | Total | U.S. States and political subdivisions securities
Assets:
Investment securities, available-for-sale	97,985	116,000
Recurring basis | Total | Mortgage-backed securities - Federal agencies
Assets:
Investment securities, available-for-sale	296,330	287,910
Recurring basis | Total | Corporate debt securities
Assets:
Investment securities, available-for-sale	44,056	31,294
Recurring basis | Total | Foreign government and other securities
Assets:
Investment securities, available-for-sale	708	710
Recurring basis | Level 1
Assets:
Investment securities, available-for-sale	27,726	27,971
Mortgages held for sale	0	0
Total	27,726	27,971
Liabilities:
Total	0	0
Recurring basis | Level 1 | Interest rate swap contracts
Assets:
Accrued income and other assets	0	0
Liabilities:
Accrued expenses and other liabilities	0	0
Recurring basis | Level 1 | U.S. Treasury and Federal agencies securities
Assets:
Investment securities, available-for-sale	27,726	27,971
Recurring basis | Level 1 | U.S. States and political subdivisions securities
Assets:
Investment securities, available-for-sale	0	0
Recurring basis | Level 1 | Mortgage-backed securities - Federal agencies
Assets:
Investment securities, available-for-sale	0	0
Recurring basis | Level 1 | Corporate debt securities
Assets:
Investment securities, available-for-sale	0	0
Recurring basis | Level 1 | Foreign government and other securities
Assets:
Investment securities, available-for-sale	0	0
Recurring basis | Level 2
Assets:
Investment securities, available-for-sale	911,487	873,197
Mortgages held for sale	8,626	13,123
Total	925,455	891,487
Liabilities:
Total	5,439	5,262
Recurring basis | Level 2 | Interest rate swap contracts
Assets:
Accrued income and other assets	5,342	5,167
Liabilities:
Accrued expenses and other liabilities	5,439	5,262
Recurring basis | Level 2 | U.S. Treasury and Federal agencies securities
Assets:
Investment securities, available-for-sale	475,271	440,148
Recurring basis | Level 2 | U.S. States and political subdivisions securities
Assets:
Investment securities, available-for-sale	95,830	113,845
Recurring basis | Level 2 | Mortgage-backed securities - Federal agencies
Assets:
Investment securities, available-for-sale	296,330	287,910
Recurring basis | Level 2 | Corporate debt securities
Assets:
Investment securities, available-for-sale	44,056	31,294
Recurring basis | Level 2 | Foreign government and other securities
Assets:
Investment securities, available-for-sale	0	0
Recurring basis | Level 3
Assets:
Investment securities, available-for-sale	2,863	2,865
Mortgages held for sale	0	0
Total	2,863	2,865
Liabilities:
Total	0	0
Recurring basis | Level 3 | Interest rate swap contracts
Assets:
Accrued income and other assets	0	0
Liabilities:
Accrued expenses and other liabilities	0	0
Recurring basis | Level 3 | U.S. Treasury and Federal agencies securities
Assets:
Investment securities, available-for-sale	0	0
Recurring basis | Level 3 | U.S. States and political subdivisions securities
Assets:
Investment securities, available-for-sale	2,155	2,155
Recurring basis | Level 3 | Mortgage-backed securities - Federal agencies
Assets:
Investment securities, available-for-sale	0	0
Recurring basis | Level 3 | Corporate debt securities
Assets:
Investment securities, available-for-sale	0	0
Recurring basis | Level 3 | Foreign government and other securities
Assets:
Investment securities, available-for-sale	$ 708	$ 710