Retirement Plans, Other Changes in Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost	$ 50	$ 58	$ 72
Amortization of actuarial gain (loss)	(15,636)	(17,079)	40,148
Income tax (expense) benefit	5,873	6,507	(15,562)
Other comprehensive income (loss) on pension and postretirement obligations	(9,713)	(10,514)	$ 24,658
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net gain (loss)	19	(483)
Amortization of prior service cost	0	0
Amortization of actuarial gain (loss)	0	(35)
Income tax (expense) benefit	(7)	199
Other comprehensive income (loss) on pension and postretirement obligations	12	(319)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net gain (loss)	(17,911)	(17,945)
Amortization of prior service cost	50	58
Amortization of actuarial gain (loss)	2,256	1,384
Income tax (expense) benefit	5,880	6,308
Other comprehensive income (loss) on pension and postretirement obligations	$ (9,725)	$ (10,195)