Accumulated Other Comprehensive Income (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net securities gains (losses)	$ 27	$ 13	$ 44	$ 26
Income tax expense	(3,385)	(3,015)	(10,592)	(16,527)
Unrealized gain (loss) on securities, net of tax	8,794	8,162	26,515	30,069
Change in funded status of post retirement benefits	184	304	551	912
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Unrealized gain (loss) on securities, net of tax	(166)	(295)	(522)	(895)
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net securities gains (losses)	27	13	44	26
Income tax expense	(9)	(4)	(15)	(9)
Unrealized gain (loss) on securities, net of tax	18	9	29	17
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Income tax expense	117	203	352	609
Unrealized gain (loss) on securities, net of tax	(184)	(304)	(551)	(912)
Change in funded status of post retirement benefits	$ (301)	$ (507)	$ (903)	$ (1,521)