Investments - Summary of unrealized loss positions (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($) item	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) item	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) position
Investments in an unrealized loss position
Total temporary impairment	$ 771,000		$ 771,000
Fair Value, AFS
12 months or more, Fair Value					$ 26,900,000
Unrealized Loss, AFS
12 months or more, Unrealized Loss					(462,000)
Fair Value, AFS and HTM
Less than 12 months, Fair Value	27,355,000		27,355,000		2,202,000
12 months or more, Fair Value	34,740,000		34,740,000		58,213,000
Unrealized Loss, AFS and HTM
Less than 12 months, Unrealized Loss	(239,000)		(239,000)		(9,000)
12 months or more, Unrealized Loss	(532,000)		(532,000)		(1,142,000)
Available-for-sale Securities
Sales of investment securities available-for-sale	1,400,000	$ 17,100,000	12,912,000	$ 54,268,000
Gains on the sale of investments available-for-sale	4	275,000	125,000	489,000
Losses on the sale of investments available-for-sale	0	4,000	0	93,000
Held-to-maturity Securities [Abstract]
Proceeds from sale of held to maturity securities	421,000		421,000		$ 0
Gain on sale of securities	$ 4,000	$ 271,000	$ 130,000	$ 396,000
U.S. Agency securities
Description and number of positions
Number of investments in an unrealized loss position, AFS	7		7		9
Fair Value, AFS
Less than 12 months, Fair Value	$ 4,993,000		$ 4,993,000		$ 996,000
12 months or more, Fair Value	14,075,000		14,075,000
Unrealized Loss, AFS
Less than 12 months, Unrealized Loss	(10,000)		(10,000)		$ (3,000)
12 months or more, Unrealized Loss	$ (24,000)		$ (24,000)
U.S. Sponsored Mortgage backed securities
Description and number of positions
Number of investments in an unrealized loss position, AFS	14		14		8
Fair Value, AFS
Less than 12 months, Fair Value	$ 13,286,000		$ 13,286,000		$ 678,000
12 months or more, Fair Value	12,606,000		12,606,000		14,824,000
Unrealized Loss, AFS
Less than 12 months, Unrealized Loss	(89,000)		(89,000)		(3,000)
12 months or more, Unrealized Loss	$ (266,000)		$ (266,000)		$ (416,000)
Municipal securities
Description and number of positions
Number of investments in an unrealized loss position, AFS | position					42
Number of investments in an unrealized loss position, HTM | item	42		42
Fair Value, HTM
Less than 12 months, Fair Value	$ 9,076,000		$ 9,076,000		$ 528,000
12 months or more, Fair Value	8,059,000		8,059,000		16,489,000
Unrealized Loss, HTM
Less than 12 months, Unrealized Loss	(140,000)		(140,000)		(3,000)
12 months or more, Unrealized Loss	$ (242,000)		$ (242,000)		$ (264,000)