Retirement Plans (Changes in Accumulated Other Comprehensive Income (Loss) Related to Retirement Plans) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)
Accumulated Other Comprehensive Income (Loss), Net of Tax
Accumulated other comprehensive income (loss) at beginning of year	$ (27,144)
Prior service costs (credits)	76
Net actuarial (income) loss	1,174
Comprehensive income (loss) adjustment	1,250
Accumulated other comprehensive income (loss) at end of year	(25,894)
Pension Plan
Accumulated Other Comprehensive Income (Loss), Net of Tax
Accumulated other comprehensive income (loss) at beginning of year	(27,291)
Prior service costs (credits)	0
Net actuarial (income) loss	1,168
Comprehensive income (loss) adjustment	1,168
Accumulated other comprehensive income (loss) at end of year	(26,123)
Postretirement Plan
Accumulated Other Comprehensive Income (Loss), Net of Tax
Accumulated other comprehensive income (loss) at beginning of year	402
Prior service costs (credits)	76
Net actuarial (income) loss	246
Comprehensive income (loss) adjustment	322
Accumulated other comprehensive income (loss) at end of year	724
Supplemental Plan
Accumulated Other Comprehensive Income (Loss), Net of Tax
Accumulated other comprehensive income (loss) at beginning of year	(255)
Prior service costs (credits)	0
Net actuarial (income) loss	(240)
Comprehensive income (loss) adjustment	(240)
Accumulated other comprehensive income (loss) at end of year	$ (495)