Pension Plans and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pension Benefits
Benefit Plans
Service cost	$ 0	$ 0
Interest cost	2,536	2,510
Expected return on plan assets	(3,058)	(3,633)
Recognized net actuarial loss (gain)	734	757
Amortization of prior service cost	47	47
Net periodic cost (benefit)	259	(319)
Other Postretirement Benefits
Benefit Plans
Service cost	472	469
Interest cost	263	276
Expected return on plan assets	0	0
Recognized net actuarial loss (gain)	(67)	0
Amortization of prior service cost	0	0
Net periodic cost (benefit)	$ 668	$ 745