Parent Company Only Financial Statements Condensed statements of cash flows (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Net income	$ 15,461,000	$ 14,722,000	$ 14,025,000
Depreciation, amortization and accretion, net	3,960,000	4,661,000	5,403,000
Increase in other assets	306,000	3,805,000	(912,000)
Increase (decrease) in other liabilities	(724,000)	401,000	1,087,000
Net cash provided by operating activities	17,777,000	24,662,000	22,889,000
Repayment of short-term debt	(1,000,000)	0	(8,250,000)
Proceeds from short-term debt	1,000,000	0	0
Conversion of preferred stock	(24,635,000)	0	0
Proceeds from issuance of preferred stock	0	0	8,250,000
Proceeds from issuance of common stock	25,123,000	1,303,000	1,255,000
Purchase of treasury stock	(1,763,000)	(4,619,000)	(3,912,000)
Dividends paid on preferred stock	(4,339,000)	(4,050,000)	(3,788,000)
Dividends paid on common stock	(2,648,000)	(2,014,000)	(2,843,000)
Net cash provided by (used in) financing activities	(21,119,000)	24,874,000	60,397,000
Decrease in cash	(13,372,000)	(17,610,000)	9,610,000
Cash and cash equivalents at beginning of period	65,102,000	82,712,000
Cash and cash equivalents at end of period	51,730,000	65,102,000	82,712,000
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	15,461,000	14,722,000	14,025,000
Depreciation, amortization and accretion, net	110,000	116,000	114,000
Dividends from subsidiaries	7,900,000	1,438,000	1,438,000
Equity in undistributed earnings of subsidiaries	(8,973,000)	(14,577,000)	(14,052,000)
Increase in other assets	(7,412,000)	(1,512,000)	(1,436,000)
Increase (decrease) in other liabilities	260,000	180,000	319,000
Net cash provided by operating activities	7,346,000	367,000	408,000
Repayment of short-term debt	0	0	(8,250,000)
Conversion of preferred stock	(24,635,000)
Proceeds from issuance of preferred stock	0	0	8,250,000
Proceeds from issuance of common stock	25,123,000	1,303,000	1,255,000
Purchase of treasury stock	(1,763,000)	(4,619,000)	(3,912,000)
Dividends paid on preferred stock	(4,339,000)	(4,050,000)	(3,788,000)
Dividends paid on common stock	(2,648,000)	(2,014,000)	(2,843,000)
Net cash provided by (used in) financing activities	(8,262,000)	(9,380,000)	(9,288,000)
Decrease in cash	(916,000)	(9,013,000)	(8,880,000)
Cash and cash equivalents at beginning of period	2,645,000	11,658,000
Cash and cash equivalents at end of period	$ 1,729,000	$ 2,645,000	$ 11,658,000