Accumulated Other Comprehensive Income (Details 2) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Jun. 30, 2016
Dec. 31, 2015
Jun. 30, 2015
Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]                
Accumulated Other Comprehensive Income (Loss), Net of Tax $ (2,412) $ (8,758) $ (2,412) $ (8,758) $ (3,493) $ (9,401) $ (14,048) $ (14,529)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent 1,081 5,290 6,989 5,771        
Net securities gains (losses) 13 9 26 23        
Income tax expense (3,015) (2,927) (16,527) (8,098)        
Unrealized gain (loss) on securities, net of tax 8,162 8,398 30,069 23,082        
Change in funded status of post retirement benefits 304 819 912 4,102        
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 313 826 929 4,117        
Unrealized gains losses on securities available-for-sale without other than temporary impairment [Member]                
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]                
Accumulated Other Comprehensive Income (Loss), Net of Tax 13,783 8,660 13,783 8,660 13,120 6,083 4,429 7,164
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent 663 4,231 7,700 1,496        
Unrealized gains losses on securities available-for-sale with other than temporary impairment [Member]                
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]                
Accumulated Other Comprehensive Income (Loss), Net of Tax 1,347 3,287 1,347 3,287 1,233 2,970 3,047 3,114
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent 114 240 (1,623) 173        
Accumulated Net Unrealized Investment Gain (Loss) [Member]                
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]                
Accumulated Other Comprehensive Income (Loss), Net of Tax 15,130 11,947 15,130 11,947 14,353 9,053 7,476 10,278
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent 777 4,471 6,077 1,669        
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) 13 9 26 23        
Income tax expense 4 2 9 8        
Unrealized gain (loss) on securities, net of tax 9 7 17 15        
Accumulated Defined Benefit Plans Adjustment [Member]                
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]                
Accumulated Other Comprehensive Income (Loss), Net of Tax (17,542) (20,705) (17,542) (20,705) $ (17,846) $ (18,454) $ (21,524) $ (24,807)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent 304 819 912 4,102        
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 203 546 609 2,735        
Unrealized gain (loss) on securities, net of tax 304 819 912 4,102        
Change in funded status of post retirement benefits $ 507 $ 1,365 $ 1,521 $ 6,837