Pension and Other Postretirement Benefits (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan, Actual Return on Plan Assets [Abstract]
Estimated future employer contributions in next fiscal year	$ 42,900
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
Actual Allocation		100.00%	100.00%
Target allocation range, maximum		100.00%	100.00%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Health care cost trend rate assumed for next fiscal year		8.00%	8.00%	8.00%
Ultimate health care cost trend rate		5.00%	5.00%	5.00%
Pension Benefits
Defined Benefit Plan, Actual Return on Plan Assets [Abstract]
Employer contributions		40,682	40,600
Participant contributions		0	0
Benefits paid		(47,204)	(37,417)
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
2014		42,900
2015		40,400
2016		40,800
2017		40,400
2018		41,500
After 2018		234,100
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year		430,894
Unrealized gains/(losses)		23,909	23,670	21,883
Balance, end of year		423,167	430,894
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost		24,119	22,215	16,497
Interest cost		23,914	24,896	22,684
Expected return on plan assets		(23,909)	(23,670)	(21,883)
Net actuarial loss		26,371	21,116	14,104
Prior service cost (gain)		1,375	1,380	1,404
Net periodic benefit cost		51,870	45,937	32,806
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate		3.95%	4.75%	5.50%
Expected return on plan assets		6.00%	6.25%	6.25%
Rate of compensation increase		4.25%	4.50%	4.25%
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan, Actual Return on Plan Assets [Abstract]
Employer contributions		4,453	5,843
Participant contributions		1,402	1,107
Benefits paid		(5,855)	(6,950)
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
2014		8,600
2015		9,400
2016		10,400
2017		11,500
2018		12,800
After 2018		88,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year		0
Unrealized gains/(losses)		0	0	0
Balance, end of year		0	0
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost		2,644	2,336	2,141
Interest cost		2,873	3,355	3,679
Expected return on plan assets		0	0	0
Net actuarial loss		1,794	1,719	1,971
Prior service cost (gain)		(2,181)	(2,181)	(2,181)
Net periodic benefit cost		5,130	5,229	5,610
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate		3.51%	4.25%	4.75%
Expected return on plan assets		0.00%	0.00%	0.00%
Rate of compensation increase		0.00%	0.00%	0.00%
Equity Securities US
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
Actual Allocation		10.00%	7.00%
Target allocation range, minimum		3.00%	3.00%
Target allocation range, maximum		15.00%	15.00%
Equity Securities International
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
Actual Allocation		9.00%	8.00%
Target allocation range, minimum		3.00%	3.00%
Target allocation range, maximum		15.00%	15.00%
Fixed Income Investments US
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
Actual Allocation		56.00%	57.00%
Target allocation range, minimum		35.00%	35.00%
Target allocation range, maximum		75.00%	75.00%
Fixed Income Investments International
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
Actual Allocation		6.00%	12.00%
Target allocation range, minimum		3.00%	3.00%
Target allocation range, maximum		10.00%	10.00%
Absolute Return
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
Actual Allocation		9.00%	9.00%
Target allocation range, minimum		5.00%	5.00%
Target allocation range, maximum		15.00%	15.00%
Real assets
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
Actual Allocation		5.00%	5.00%
Target allocation range, minimum		3.00%	3.00%
Target allocation range, maximum		10.00%	10.00%
Private equity
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
Actual Allocation		1.00%	1.00%
Target allocation range, minimum		0.00%	0.00%
Target allocation range, maximum		3.00%	3.00%
Short-term Investments
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
Actual Allocation		4.00%	1.00%
Target allocation range, minimum		0.00%	0.00%
Target allocation range, maximum		3.00%	3.00%
Quoted Prices in Active Markets for Identical Inputs (Level 1)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		265,082	264,410
Quoted Prices in Active Markets for Identical Inputs (Level 1) | Corporate stocks
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		20,176	15,609
Quoted Prices in Active Markets for Identical Inputs (Level 1) | Mutual funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		11,169	6,505
Quoted Prices in Active Markets for Identical Inputs (Level 1) | Corporate stocks
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		1,101	544
Quoted Prices in Active Markets for Identical Inputs (Level 1) | Mutual funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		38,246	33,603
Quoted Prices in Active Markets for Identical Inputs (Level 1) | Corporate debt
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		108,844	120,457
Quoted Prices in Active Markets for Identical Inputs (Level 1) | US government debt
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		38,870	37,979
Quoted Prices in Active Markets for Identical Inputs (Level 1) | Mutual funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		22,756	17,988
Quoted Prices in Active Markets for Identical Inputs (Level 1) | Foreign Corporate Debt Securities
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		23,920	31,725
Quoted Prices in Active Markets for Identical Inputs (Level 1) | Commingled funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year			0
Quoted Prices in Active Markets for Identical Inputs (Level 1) | Absolute Return
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Quoted Prices in Active Markets for Identical Inputs (Level 1) | Real assets
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Quoted Prices in Active Markets for Identical Inputs (Level 1) | Private equity
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Quoted Prices in Active Markets for Identical Inputs (Level 1) | Short-term Investments
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		100,107	83,929
Significant Other Observable Inputs (Level 2) | Corporate stocks
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Other Observable Inputs (Level 2) | Mutual funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		11,754	8,871
Significant Other Observable Inputs (Level 2) | Corporate stocks
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Other Observable Inputs (Level 2) | Mutual funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Other Observable Inputs (Level 2) | Corporate debt
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Other Observable Inputs (Level 2) | US government debt
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Other Observable Inputs (Level 2) | Mutual funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		63,916	68,017
Significant Other Observable Inputs (Level 2) | Foreign Corporate Debt Securities
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Other Observable Inputs (Level 2) | Commingled funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year			0
Significant Other Observable Inputs (Level 2) | Absolute Return
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Other Observable Inputs (Level 2) | Real assets
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		8,455	7,041
Significant Other Observable Inputs (Level 2) | Private equity
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Other Observable Inputs (Level 2) | Short-term Investments
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		15,982	0
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year			84,487
Realized gains/(losses)			1,445
Unrealized gains/(losses)			3,570
Transfers			(7,041)
Purchases			102,621
Sales			(102,527)
Balance, end of year		57,978	82,555
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Expected return on plan assets			(3,570)
Significant Unobservable Inputs (Level 3) | Pension Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year		82,555
Realized gains/(losses)		6,568
Unrealized gains/(losses)		(2,172)
Purchases		30,900
Sales		(59,873)
Balance, end of year		57,978
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Expected return on plan assets		2,172
Significant Unobservable Inputs (Level 3) | Corporate stocks
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Unobservable Inputs (Level 3) | Mutual funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Unobservable Inputs (Level 3) | Corporate stocks
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Unobservable Inputs (Level 3) | Mutual funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Unobservable Inputs (Level 3) | Corporate debt
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Unobservable Inputs (Level 3) | US government debt
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Unobservable Inputs (Level 3) | Mutual funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Unobservable Inputs (Level 3) | Fixed Income Investments International | Pension Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0
Significant Unobservable Inputs (Level 3) | Foreign Corporate Debt Securities
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		0	0
Significant Unobservable Inputs (Level 3) | Commingled funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year			18,314
Realized gains/(losses)			35
Unrealized gains/(losses)			1,841
Transfers			0
Purchases			2,000
Sales			(127)
Balance, end of year			22,063
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Expected return on plan assets			(1,841)
Significant Unobservable Inputs (Level 3) | Commingled funds | Pension Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year		22,063
Realized gains/(losses)		5,721
Unrealized gains/(losses)		(6,629)
Purchases		0
Sales		(21,155)
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Expected return on plan assets		6,629
Significant Unobservable Inputs (Level 3) | Absolute Return
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year			36,738
Realized gains/(losses)			1,125
Unrealized gains/(losses)			756
Transfers			0
Purchases			3,505
Sales			(4,835)
Balance, end of year		39,448	37,289
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Expected return on plan assets			(756)
Significant Unobservable Inputs (Level 3) | Absolute Return | Pension Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year		37,289
Realized gains/(losses)		831
Unrealized gains/(losses)		2,344
Purchases		30,900
Sales		(31,916)
Balance, end of year		39,448
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Expected return on plan assets		(2,344)
Significant Unobservable Inputs (Level 3) | Real assets
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year			17,451
Realized gains/(losses)			54
Unrealized gains/(losses)			1,320
Transfers			(7,041)
Purchases			1,239
Sales			(321)
Balance, end of year		14,737	12,702
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Expected return on plan assets			(1,320)
Significant Unobservable Inputs (Level 3) | Real assets | Pension Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year		12,702
Realized gains/(losses)		16
Unrealized gains/(losses)		2,127
Purchases		0
Sales		(108)
Balance, end of year		14,737
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Expected return on plan assets		(2,127)
Significant Unobservable Inputs (Level 3) | Private equity
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year			4,303
Realized gains/(losses)			231
Unrealized gains/(losses)			(347)
Transfers			0
Purchases			183
Sales			(563)
Balance, end of year		3,793	3,807
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Expected return on plan assets			347
Significant Unobservable Inputs (Level 3) | Private equity | Pension Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year		3,807
Realized gains/(losses)		0
Unrealized gains/(losses)		(14)
Purchases		0
Sales		0
Balance, end of year		3,793
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Expected return on plan assets		14
Significant Unobservable Inputs (Level 3) | Short-term Investments
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year			7,681
Realized gains/(losses)			0
Unrealized gains/(losses)			0
Transfers			0
Purchases			95,694
Sales			(96,681)
Balance, end of year		0	6,694
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Expected return on plan assets			0
Significant Unobservable Inputs (Level 3) | Short-term Investments | Pension Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year		6,694
Realized gains/(losses)		0
Unrealized gains/(losses)		0
Purchases		0
Sales		(6,694)
Balance, end of year		0
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Expected return on plan assets		0
Estimate of Fair Value, Fair Value Disclosure
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		423,167	430,894
Estimate of Fair Value, Fair Value Disclosure | Corporate stocks
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		20,176	15,609
Estimate of Fair Value, Fair Value Disclosure | Mutual funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		22,923	15,376
Estimate of Fair Value, Fair Value Disclosure | Corporate stocks
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		1,101	544
Estimate of Fair Value, Fair Value Disclosure | Mutual funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		38,246	33,603
Estimate of Fair Value, Fair Value Disclosure | Corporate debt
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		108,844	120,457
Estimate of Fair Value, Fair Value Disclosure | US government debt
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		38,870	37,979
Estimate of Fair Value, Fair Value Disclosure | Mutual funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		86,672	86,005
Estimate of Fair Value, Fair Value Disclosure | Foreign Corporate Debt Securities
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		23,920	31,725
Estimate of Fair Value, Fair Value Disclosure | Commingled funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year			22,063
Estimate of Fair Value, Fair Value Disclosure | Absolute Return
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		39,448	37,289
Estimate of Fair Value, Fair Value Disclosure | Real assets
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		23,192	19,743
Estimate of Fair Value, Fair Value Disclosure | Private equity
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		3,793	3,807
Estimate of Fair Value, Fair Value Disclosure | Short-term Investments
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, end of year		$ 15,982	$ 6,694
January 1, 2019
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Ultimate health care cost trend rate		5.00%