Pension and Other Postretirement Benefits - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Requisite service period			3 years
Contributions by employer	$ 10,002	$ 10,002	$ 21,534	$ 22,862
Estimated future contributions in remainder of 2015			$ 20,003