Employee Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 01, 2012	Jan. 24, 2012
Amounts recognized on balance sheet:
Other current liabilities	$ (2,660,000)	$ (2,611,000)
Employee benefit obligations	(99,366,000)	(80,321,000)
Pension Benefits
Pension and Other Postretirement Benefits
Reduction in the net recorded liability				33,400,000
Change in projected benefit obligation:
Obligation at beginning of period	220,330,000	245,211,000
Service cost			1,488,000
Interest cost	8,844,000	8,344,000	10,008,000
Actuarial (gain) loss	26,643,000	(16,236,000)
Benefits paid	(7,312,000)	(16,989,000)
Obligation at end of period	248,505,000	220,330,000	245,211,000
Change in plan assets:
Fair value of plan assets at beginning of period	188,386,000	164,426,000
Actual return on plan assets	15,562,000	29,056,000
Employer contributions	9,673,000	11,893,000
Benefits paid	(7,312,000)	(16,989,000)
Fair value of plan assets at end of period	206,309,000	188,386,000	164,426,000
Funded status:
Plan assets less than projected benefit obligation	(42,196,000)	(31,944,000)
Amounts recognized on balance sheet:
Employee benefit obligations	(42,196,000)	(31,944,000)
Net amount recognized	(42,196,000)	(31,944,000)
Actuarial gain (loss) recognized in accumulated other comprehensive income (loss)	(27,728,000)	(3,783,000)
Actuarial assumptions:
Defined Benefit Plan, Net Periodic Benefit Cost	(3,685,000)	(2,888,000)	434,000
Assumed health care cost trend rate, ultimate year	100,000
Pension Benefits | Minimum
Actuarial assumptions:
Discount rate (as a percent)	3.70%	4.40%
Pension Benefits | Maximum
Actuarial assumptions:
Discount rate (as a percent)	3.74%	4.62%
Other Postretirement Benefits
Change in projected benefit obligation:
Obligation at beginning of period	50,988,000	53,630,000
Service cost	897,000	1,047,000	965,000
Interest cost	2,384,000	2,089,000	2,362,000
Actuarial (gain) loss	7,239,000	(4,044,000)
Benefits paid	(1,678,000)	(1,734,000)
Obligation at end of period	59,830,000	50,988,000	53,630,000
Change in plan assets:
Employer contributions	1,678,000	1,734,000
Benefits paid	(1,678,000)	(1,734,000)
Funded status:
Plan assets less than projected benefit obligation	(59,830,000)	(50,988,000)
Amounts recognized on balance sheet:
Other current liabilities	(2,660,000)	(2,611,000)
Employee benefit obligations	(57,170,000)	(48,377,000)
Net amount recognized	(59,830,000)	(50,988,000)
Actuarial gain (loss) recognized in accumulated other comprehensive income (loss)	(10,931,000)	(3,752,000)
Actuarial assumptions:
Defined Benefit Plan, Net Periodic Benefit Cost	3,341,000	3,492,000	3,445,000
Assumed health care cost trend rate, current (as a percent)	7.00%	7.50%	7.50%
Assumed health care cost trend rate, current (as a percent)	6.75%	7.00%
Assumed health care cost trend rate, ultimate (as a percent)	5.00%	5.00%	5.00%
Assumed health care cost trend rate, ultimate (as a percent)	5.00%	5.00%
Assumed health care cost trend rate, ultimate year	600,000
Other Postretirement Benefits | Minimum
Actuarial assumptions:
Discount rate (as a percent)	3.97%	4.75%
Other Postretirement Benefits | Maximum
Actuarial assumptions:
Discount rate (as a percent)	4.15%	5.01%
Union Pension Plan
Pension and Other Postretirement Benefits
Reduction in the net recorded liability				$ 30,200,000
Actuarial assumptions:
Discount rate (as a percent)					4.54%