Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Fair Value Measurements
Transfers between levels of fair value hierarchy	$ 0
Financial assets and financial liabilities measured at fair value
Securities available for sale	852,836	841,310
Impaired loans	30,738	34,060
OREO	1,937	2,133
U.S. Treasury securities
Financial assets and financial liabilities measured at fair value
Securities available for sale	50,670	102,640
Obligations of U.S. government corporations and agencies
Financial assets and financial liabilities measured at fair value
Securities available for sale	231,245	257,411
Obligations of states and political subdivisions
Financial assets and financial liabilities measured at fair value
Securities available for sale	253,722	272,152
Residential mortgage-backed securities
Financial assets and financial liabilities measured at fair value
Securities available for sale	269,454	177,735
Corporate debt securities
Financial assets and financial liabilities measured at fair value
Securities available for sale	42,756	25,506
Mutual funds and other equity securities
Financial assets and financial liabilities measured at fair value
Securities available for sale	4,989	5,866
Recurring basis | Level 1 Inputs | Mutual funds and other equity securities
Financial assets and financial liabilities measured at fair value
Securities available for sale	4,989	5,866
Recurring basis | Level 2 Inputs | Foreign currency forward contracts
Financial assets and financial liabilities measured at fair value
Derivative assets	2
Derivative liabilities	3
Recurring basis | Level 2 Inputs | U.S. Treasury securities
Financial assets and financial liabilities measured at fair value
Securities available for sale	50,670	102,640
Recurring basis | Level 2 Inputs | Obligations of U.S. government corporations and agencies
Financial assets and financial liabilities measured at fair value
Securities available for sale	231,245	257,411
Recurring basis | Level 2 Inputs | Obligations of states and political subdivisions
Financial assets and financial liabilities measured at fair value
Securities available for sale	253,722	272,152
Recurring basis | Level 2 Inputs | Residential mortgage-backed securities
Financial assets and financial liabilities measured at fair value
Securities available for sale	269,454	177,735
Recurring basis | Level 2 Inputs | Corporate debt securities
Financial assets and financial liabilities measured at fair value
Securities available for sale	42,756	25,506
Recurring basis | Total Fair Value | Foreign currency forward contracts
Financial assets and financial liabilities measured at fair value
Derivative assets	2
Derivative liabilities	3
Recurring basis | Total Fair Value | U.S. Treasury securities
Financial assets and financial liabilities measured at fair value
Securities available for sale	50,670	102,640
Recurring basis | Total Fair Value | Obligations of U.S. government corporations and agencies
Financial assets and financial liabilities measured at fair value
Securities available for sale	231,245	257,411
Recurring basis | Total Fair Value | Obligations of states and political subdivisions
Financial assets and financial liabilities measured at fair value
Securities available for sale	253,722	272,152
Recurring basis | Total Fair Value | Residential mortgage-backed securities
Financial assets and financial liabilities measured at fair value
Securities available for sale	269,454	177,735
Recurring basis | Total Fair Value | Corporate debt securities
Financial assets and financial liabilities measured at fair value
Securities available for sale	42,756	25,506
Recurring basis | Total Fair Value | Mutual funds and other equity securities
Financial assets and financial liabilities measured at fair value
Securities available for sale	4,989	5,866
Non-recurring basis | Level 3 Inputs
Financial assets and financial liabilities measured at fair value
Impaired loans	4,227	5,491
OREO	1,137	1,134
Non-recurring basis | Total Fair Value
Financial assets and financial liabilities measured at fair value
Impaired loans	4,227	5,491
OREO	$ 1,137	$ 1,134