Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Pension and Other Postretirement Benefits
Net periodic benefit cost (income)	$ (553)	$ (1,299)
Settlement loss		$ 850
Discount rate used to measure the plan obligations (as percent)		3.57%
Other comprehensive income due to the results of fair value of plan assets		$ 2,200
Actuarial assumptions:
Discount rate (as a percent)		3.54%
Union employees
Pension and Other Postretirement Benefits
Lump-sum benefits to plan participants in full settlement of obligations		$ 6,000
Non-union employees
Pension and Other Postretirement Benefits
Lump-sum benefits to plan participants in full settlement of obligations		600
Pension
Pension and Other Postretirement Benefits
Interest cost	1,996	2,073
Expected asset return	(2,678)	(3,394)
Amortization of loss	129	22
Total benefit income	(553)	(449)
Expected company contribution			$ 9,300
Company contribution	1,900
Other Postretirement Benefits
Pension and Other Postretirement Benefits
Service cost	259	259
Interest cost	655	589
Amortization of loss	119	149
Net periodic benefit cost (income)	$ 1,033	$ 997