Pension Plan and Postretirement Benefits Other Than Pension (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Weighted average assumptions used to determine net periodic benefit cost
Expected return on plan assets (as a percent)	7.75%
Pension Benefits
Components of net periodic benefit cost:
Service cost	$ 10,084,000	$ 11,011,000	$ 9,373,000
Interest cost	8,395,000	7,711,000	7,570,000
Expected return on plan assets	(14,016,000)	(11,185,000)	(8,799,000)
Actuarial loss amortization	1,496,000	4,567,000	4,563,000
Prior service cost amortization	468,000	555,000	555,000
Transition obligation amortization	5,000	5,000	5,000
Net periodic benefit cost	6,432,000	12,664,000	13,267,000
Amounts that will be amortized from accumulated other comprehensive income into net periodic benefit cost in next fiscal year
Estimated net gain (loss) that will be amortized from accumulated other comprehensive income into net periodic benefit cost	(5,000,000)
Estimated prior service cost that will be amortized from accumulated other comprehensive income into net periodic benefit cost	459,000
Estimated transition obligation that will be amortized from accumulated other comprehensive income into net periodic benefit cost	5,000
Weighted average assumptions used to determine net periodic benefit cost
Discount rate (as a percent)	4.97%	4.22%	4.99%
Expected return on plan assets (as a percent)	7.75%	7.75%	7.75%
Rate of compensation increase (as a percent)	5.12%	3.99%	4.04%
Expected benefit payments
2015	6,813,000
2016	8,743,000
2017	9,929,000
2018	10,066,000
2019	12,161,000
2020 through 2024	74,734,000
Total	122,446,000
Expected contribution in the next fiscal year	20,000,000
Pension Benefits | Segment Discontinued Operations
Components of net periodic benefit cost:
Net periodic benefit cost			749,000
Other Postretirement Benefits
Components of net periodic benefit cost:
Service cost	719,000	788,000	693,000
Interest cost	397,000	361,000	400,000
Actuarial loss amortization	(17,000)		12,000
Prior service cost amortization	55,000	55,000	55,000
Net periodic benefit cost	1,154,000	1,204,000	1,160,000
Amounts that will be amortized from accumulated other comprehensive income into net periodic benefit cost in next fiscal year
Estimated net gain (loss) that will be amortized from accumulated other comprehensive income into net periodic benefit cost	19,000
Weighted average assumptions used to determine net periodic benefit cost
Discount rate (as a percent)	4.94%	4.18%	5.00%
Expected benefit payments
2015	279,000
2016	341,000
2017	378,000
2018	478,000
2019	558,000
2020 through 2024	3,839,000
Total	5,873,000
Contributions by participants	381,000	321,000	337,000
Other Postretirement Benefits | Segment Discontinued Operations
Components of net periodic benefit cost:
Net periodic benefit cost			$ 749,000