Securities Available-for-Sale - Fair Value and Age of Gross Unrealized Losses by Investment Category (Details) $ in Thousands	Sep. 30, 2017 USD ($) security	Dec. 31, 2016 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	30	31
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 258,806	$ 267,500
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (2,211)	$ (3,472)
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	1	0
Available-for-sale Securities, 12 Months or More, Fair Value	$ 7,586	$ 0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ (232)	$ 0
Available-for-sale, Securities, Number of Positions \| security	31	31
Available-for-sale Securities, Fair Value, Total	$ 266,392	$ 267,500
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (2,443)	$ (3,472)
U.S. treasury securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	2	1
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 14,903	$ 9,811
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (38)	$ (127)
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	0	0
Available-for-sale Securities, 12 Months or More, Fair Value	$ 0	$ 0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ 0
Available-for-sale, Securities, Number of Positions \| security	2	1
Available-for-sale Securities, Fair Value, Total	$ 14,903	$ 9,811
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (38)	$ (127)
Obligations of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	8	7
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 72,102	$ 62,483
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (357)	$ (383)
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	0	0
Available-for-sale Securities, 12 Months or More, Fair Value	$ 0	$ 0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ 0
Available-for-sale, Securities, Number of Positions \| security	8	7
Available-for-sale Securities, Fair Value, Total	$ 72,102	$ 62,483
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (357)	$ (383)
Collateralized mortgage obligations of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	8	10
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 62,408	$ 83,031
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (608)	$ (734)
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	0	0
Available-for-sale Securities, 12 Months or More, Fair Value	$ 0	$ 0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ 0
Available-for-sale, Securities, Number of Positions \| security	8	10
Available-for-sale Securities, Fair Value, Total	$ 62,408	$ 83,031
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (608)	$ (734)
Residential mortgage-backed securities of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	2	2
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 9,071	$ 10,022
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (151)	$ (232)
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	0	0
Available-for-sale Securities, 12 Months or More, Fair Value	$ 0	$ 0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ 0
Available-for-sale, Securities, Number of Positions \| security	2	2
Available-for-sale Securities, Fair Value, Total	$ 9,071	$ 10,022
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (151)	$ (232)
Commercial mortgage-backed securities of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	10	10
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 100,322	$ 96,576
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (1,057)	$ (1,950)
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	1	0
Available-for-sale Securities, 12 Months or More, Fair Value	$ 7,586	$ 0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ (232)	$ 0
Available-for-sale, Securities, Number of Positions \| security	11	10
Available-for-sale Securities, Fair Value, Total	$ 107,908	$ 96,576
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (1,289)	$ (1,950)
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	0	1
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 0	$ 5,577
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ 0	$ (46)
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	0	0
Available-for-sale Securities, 12 Months or More, Fair Value	$ 0	$ 0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ 0
Available-for-sale, Securities, Number of Positions \| security	0	1
Available-for-sale Securities, Fair Value, Total	$ 0	$ 5,577
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 0	$ (46)
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	30	31
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 258,806	$ 267,500
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ (2,211)	$ (3,472)
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	1	0
Available-for-sale Securities, 12 Months or More, Fair Value	$ 7,586	$ 0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ (232)	$ 0
Available-for-sale, Securities, Number of Positions \| security	31	31
Available-for-sale Securities, Fair Value, Total	$ 266,392	$ 267,500
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (2,443)	$ (3,472)
Marketable equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities, Less Than 12 Months, Number of Positions \| security	0	0
Available-for-sale Securities, Less Than 12 Months, Fair Value	$ 0	$ 0
Available-for-sale Securities, Less Than 12 Months, Unrealized Losses	$ 0	$ 0
Available-for-sale, Securities, 12 Months or More, Number of Positions \| security	0	0
Available-for-sale Securities, 12 Months or More, Fair Value	$ 0	$ 0
Available-for-sale Securities, 12 Months or More, Unrealized Losses	$ 0	$ 0
Available-for-sale, Securities, Number of Positions \| security	0	0
Available-for-sale Securities, Fair Value, Total	$ 0	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 0	$ 0

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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