Fair Value Measurements (Details 2) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Assets:
Investment securities, available-for-sale	$ 786,471	$ 791,118
Trading account securities	211	205
Mortgages held for sale	14,782	13,604
Liabilities:
Accrued expenses and other liabilities	131,272	138,012
U.S. Treasury and Federal agencies securities
Assets:
Investment securities, available-for-sale	385,914	373,503
U.S. States and political subdivisions securities
Assets:
Investment securities, available-for-sale	123,708	124,688
Mortgage-backed securities - Federal agencies
Assets:
Investment securities, available-for-sale	235,250	253,008
Corporate debt securities
Assets:
Investment securities, available-for-sale	33,577	31,932
Foreign government and other securities
Assets:
Investment securities, available-for-sale	807	811
Total debt securities
Assets:
Investment securities, available-for-sale	779,256	783,942
Marketable equity securities
Assets:
Investment securities, available-for-sale	7,215	7,176
Total
Assets:
Investment securities, available-for-sale	786,471	791,118
Mortgages held for sale	14,782	13,604
Level 1
Assets:
Investment securities, available-for-sale	27,160	26,984
Mortgages held for sale	0	0
Level 2
Assets:
Investment securities, available-for-sale	753,060	756,857
Mortgages held for sale	14,782	13,604
Level 3
Assets:
Investment securities, available-for-sale	6,251	7,277
Mortgages held for sale	0	0
Recurring basis | Total
Assets:
Investment securities, available-for-sale	786,471	791,118
Trading account securities	211	205
Mortgages held for sale	14,782	13,604
Total	809,650	814,052
Liabilities:
Total	8,342	9,302
Recurring basis | Total | Interest rate swap contracts
Assets:
Accrued income and other assets	8,186	9,125
Liabilities:
Accrued expenses and other liabilities	8,342	9,302
Recurring basis | Total | U.S. Treasury and Federal agencies securities
Assets:
Investment securities, available-for-sale	385,914	373,503
Recurring basis | Total | U.S. States and political subdivisions securities
Assets:
Investment securities, available-for-sale	123,708	124,688
Recurring basis | Total | Mortgage-backed securities - Federal agencies
Assets:
Investment securities, available-for-sale	235,250	253,008
Recurring basis | Total | Corporate debt securities
Assets:
Investment securities, available-for-sale	33,577	31,932
Recurring basis | Total | Foreign government and other securities
Assets:
Investment securities, available-for-sale	807	811
Recurring basis | Total | Total debt securities
Assets:
Investment securities, available-for-sale	779,256	783,942
Recurring basis | Total | Marketable equity securities
Assets:
Investment securities, available-for-sale	7,215	7,176
Recurring basis | Level 1
Assets:
Investment securities, available-for-sale	27,160	26,984
Trading account securities	211	205
Mortgages held for sale	0	0
Total	27,371	27,189
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	19,945	19,808
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 1 | Total debt securities
Assets:
Investment securities, available-for-sale	19,945	19,808
Recurring basis | Level 1 | Marketable equity securities
Assets:
Investment securities, available-for-sale	7,215	7,176
Recurring basis | Level 2
Assets:
Investment securities, available-for-sale	753,060	756,857
Trading account securities	0	0
Mortgages held for sale	14,782	13,604
Total	776,028	779,586
Liabilities:
Total	8,342	9,302
Recurring basis | Level 2 | Interest rate swap contracts
Assets:
Accrued income and other assets	8,186	9,125
Liabilities:
Accrued expenses and other liabilities	8,342	9,302
Recurring basis | Level 2 | U.S. Treasury and Federal agencies securities
Assets:
Investment securities, available-for-sale	365,969	353,695
Recurring basis | Level 2 | U.S. States and political subdivisions securities
Assets:
Investment securities, available-for-sale	118,264	118,222
Recurring basis | Level 2 | Mortgage-backed securities - Federal agencies
Assets:
Investment securities, available-for-sale	235,250	253,008
Recurring basis | Level 2 | Corporate debt securities
Assets:
Investment securities, available-for-sale	33,577	31,932
Recurring basis | Level 2 | Foreign government and other securities
Assets:
Investment securities, available-for-sale	0	0
Recurring basis | Level 2 | Total debt securities
Assets:
Investment securities, available-for-sale	753,060	756,857
Recurring basis | Level 2 | Marketable equity securities
Assets:
Investment securities, available-for-sale	0	0
Recurring basis | Level 3
Assets:
Investment securities, available-for-sale	6,251	7,277
Trading account securities	0	0
Mortgages held for sale	0	0
Total	6,251	7,277
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	5,444	6,466
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	807	811
Recurring basis | Level 3 | Total debt securities
Assets:
Investment securities, available-for-sale	6,251	7,277
Recurring basis | Level 3 | Marketable equity securities
Assets:
Investment securities, available-for-sale	$ 0	$ 0