Accumulated Other Comprehensive Income (Loss) - Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Pension Plan Adjustments
Accumulated Other Comprehensive Income (Loss)
Income tax benefit included in accumulated other comprehensive loss	$ 17,700	$ 17,100	$ 17,400
Components of income tax expense (benefit) included in other comprehensive income (loss)
Income tax expense (benefit) included in other comprehensive income (loss)	(647)	183	(7,202)
Derivatives
Accumulated Other Comprehensive Income (Loss)
Income tax benefit included in accumulated other comprehensive loss		100
Income tax expense in accumulated other comprehensive income	400		500
Components of income tax expense (benefit) included in other comprehensive income (loss)
Income tax expense (benefit) included in other comprehensive income (loss)	$ 519	$ (521)	$ 184