Accumulated Other Comprehensive Income (Loss) - Income Tax Expense (Benefit) (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Pension Plan Adjustments
Accumulated Other Comprehensive Income (Loss)
Income tax benefits in accumulated other comprehensive loss	$ 17,100	$ 17,400	$ 9,700
Components of income tax expense (benefit) included in other comprehensive income (loss)
Income tax expense (benefit) included in other comprehensive income (loss)	183	(7,202)	9,840
Derivatives
Accumulated Other Comprehensive Income (Loss)
Income tax benefits in accumulated other comprehensive loss	100
Income tax expense in accumulated other comprehensive loss		500	300
Components of income tax expense (benefit) included in other comprehensive income (loss)
Income tax expense (benefit) included in other comprehensive income (loss)	$ (521)	$ 184	$ 358