Fair Value Measurement - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers between Level 1 to Level 2	$ 0	$ 0
ASSETS
Total securities available-for-sale	689,388,000	693,487,000
U.S. treasury securities
ASSETS
Total securities available-for-sale	24,886,000	24,811,000
Obligations of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	211,434,000	232,179,000
Collateralized mortgage obligations of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	120,203,000	129,777,000
Residential mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	34,611,000	37,358,000
Commercial mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	162,413,000	125,604,000
Obligations of states and political subdivisions
ASSETS
Total securities available-for-sale	131,106,000	132,509,000
Marketable equity securities
ASSETS
Total securities available-for-sale	4,735,000	11,249,000
Fair Value Measurements, Recurring
ASSETS
Total securities available-for-sale	689,388,000	693,487,000
Trading securities held in a Rabbi Trust	4,790,000	4,410,000
Total securities	694,178,000	697,897,000
Total Assets	700,090,000	705,093,000
LIABILITIES
Total Liabilities	5,423,000	6,985,000
Fair Value Measurements, Recurring | Interest rate swap contracts - commercial loans
ASSETS
Derivative financial assets	5,442,000	6,960,000
LIABILITIES
Derivative financial liabilities	5,423,000	6,958,000
Fair Value Measurements, Recurring | Interest rate lock commitments - mortgage loans
ASSETS
Derivative financial assets	456,000	236,000
Fair Value Measurements, Recurring | Forward sale contracts - mortgage loans
ASSETS
Derivative financial assets	14,000
LIABILITIES
Derivative financial liabilities		27,000
Fair Value Measurements, Recurring | U.S. treasury securities
ASSETS
Total securities available-for-sale	24,886,000	24,811,000
Fair Value Measurements, Recurring | Obligations of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	211,434,000	232,179,000
Fair Value Measurements, Recurring | Collateralized mortgage obligations of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	120,203,000	129,777,000
Fair Value Measurements, Recurring | Residential mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	34,611,000	37,358,000
Fair Value Measurements, Recurring | Commercial mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	162,413,000	125,604,000
Fair Value Measurements, Recurring | Obligations of states and political subdivisions
ASSETS
Total securities available-for-sale	131,106,000	132,509,000
Fair Value Measurements, Recurring | Marketable equity securities
ASSETS
Total securities available-for-sale	4,735,000	11,249,000
Fair Value Measurements, Recurring | Level 1
ASSETS
Total securities available-for-sale	0	0
Trading securities held in a Rabbi Trust	4,790,000	4,410,000
Total securities	4,790,000	4,410,000
Total Assets	4,790,000	4,410,000
LIABILITIES
Total Liabilities	0	0
Fair Value Measurements, Recurring | Level 1 | Interest rate swap contracts - commercial loans
ASSETS
Derivative financial assets	0	0
LIABILITIES
Derivative financial liabilities	0	0
Fair Value Measurements, Recurring | Level 1 | Interest rate lock commitments - mortgage loans
ASSETS
Derivative financial assets	0	0
Fair Value Measurements, Recurring | Level 1 | Forward sale contracts - mortgage loans
ASSETS
Derivative financial assets	0
LIABILITIES
Derivative financial liabilities		0
Fair Value Measurements, Recurring | Level 1 | U.S. treasury securities
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring | Level 1 | Obligations of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring | Level 1 | Collateralized mortgage obligations of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring | Level 1 | Residential mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring | Level 1 | Commercial mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring | Level 1 | Obligations of states and political subdivisions
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring | Level 1 | Marketable equity securities
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring | Level 2
ASSETS
Total securities available-for-sale	689,388,000	693,487,000
Trading securities held in a Rabbi Trust	0	0
Total securities	689,388,000	693,487,000
Total Assets	695,300,000	700,683,000
LIABILITIES
Total Liabilities	5,423,000	6,985,000
Fair Value Measurements, Recurring | Level 2 | Interest rate swap contracts - commercial loans
ASSETS
Derivative financial assets	5,442,000	6,960,000
LIABILITIES
Derivative financial liabilities	5,423,000	6,958,000
Fair Value Measurements, Recurring | Level 2 | Interest rate lock commitments - mortgage loans
ASSETS
Derivative financial assets	456,000	236,000
Fair Value Measurements, Recurring | Level 2 | Forward sale contracts - mortgage loans
ASSETS
Derivative financial assets	14,000
LIABILITIES
Derivative financial liabilities		27,000
Fair Value Measurements, Recurring | Level 2 | U.S. treasury securities
ASSETS
Total securities available-for-sale	24,886,000	24,811,000
Fair Value Measurements, Recurring | Level 2 | Obligations of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	211,434,000	232,179,000
Fair Value Measurements, Recurring | Level 2 | Collateralized mortgage obligations of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	120,203,000	129,777,000
Fair Value Measurements, Recurring | Level 2 | Residential mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	34,611,000	37,358,000
Fair Value Measurements, Recurring | Level 2 | Commercial mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	162,413,000	125,604,000
Fair Value Measurements, Recurring | Level 2 | Obligations of states and political subdivisions
ASSETS
Total securities available-for-sale	131,106,000	132,509,000
Fair Value Measurements, Recurring | Level 2 | Marketable equity securities
ASSETS
Total securities available-for-sale	4,735,000	11,249,000
Fair Value Measurements, Recurring | Level 3
ASSETS
Total securities available-for-sale	0	0
Trading securities held in a Rabbi Trust	0	0
Total securities	0	0
Total Assets	0	0
LIABILITIES
Total Liabilities	0	0
Fair Value Measurements, Recurring | Level 3 | Interest rate swap contracts - commercial loans
ASSETS
Derivative financial assets	0	0
LIABILITIES
Derivative financial liabilities	0	0
Fair Value Measurements, Recurring | Level 3 | Interest rate lock commitments - mortgage loans
ASSETS
Derivative financial assets	0	0
Fair Value Measurements, Recurring | Level 3 | Forward sale contracts - mortgage loans
ASSETS
Derivative financial assets	0
LIABILITIES
Derivative financial liabilities		0
Fair Value Measurements, Recurring | Level 3 | U.S. treasury securities
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring | Level 3 | Obligations of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring | Level 3 | Collateralized mortgage obligations of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring | Level 3 | Residential mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring | Level 3 | Commercial mortgage-backed securities of U.S. government corporations and agencies
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring | Level 3 | Obligations of states and political subdivisions
ASSETS
Total securities available-for-sale	0	0
Fair Value Measurements, Recurring | Level 3 | Marketable equity securities
ASSETS
Total securities available-for-sale	$ 0	$ 0