Pension and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Health care cost trend rate assumed for next fiscal year	7.00%
Ultimate health care cost trend rate	5.00%
Estimated nonqualified benefits in next fiscal year	$ 1,635
Estimated future employer contributions in next fiscal year	$ 40,000
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Actual Allocation	100.00%	100.00%
Target allocation range, maximum	100.00%	100.00%
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	$ 470,165
Balance, end of year	$ 447,258	$ 470,165
Equity Securities US
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Actual Allocation	12.00%	9.00%
Target allocation range, minimum	3.00%	3.00%
Target allocation range, maximum	15.00%	15.00%
Corporate stocks
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	$ 17,092
Balance, end of year	18,908	$ 17,092
Mutual funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	26,739
Balance, end of year	$ 33,858	$ 26,739
Equity Securities International
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Actual Allocation	11.00%	9.00%
Target allocation range, minimum	3.00%	3.00%
Target allocation range, maximum	15.00%	15.00%
Corporate stocks
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	$ 946
Balance, end of year	1,410	$ 946
Mutual funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	43,710
Balance, end of year	$ 46,594	$ 43,710
Fixed Income Investments US
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Actual Allocation	59.00%	61.00%
Target allocation range, minimum	35.00%	35.00%
Target allocation range, maximum	75.00%	75.00%
Corporate debt
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	$ 128,033
Balance, end of year	131,109	$ 128,033
US government debt
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	52,674
Balance, end of year	42,720	52,674
Mutual funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	104,324
Balance, end of year	$ 93,342	$ 104,324
Fixed Income Investments, Foreign [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Actual Allocation	6.00%	6.00%
Target allocation range, minimum	3.00%	3.00%
Target allocation range, maximum	10.00%	10.00%
Foreign Corporate Debt Securities
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	$ 27,784
Balance, end of year	$ 26,044	$ 27,784
Absolute Return
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Actual Allocation	7.00%	7.00%
Target allocation range, minimum	5.00%	5.00%
Target allocation range, maximum	15.00%	15.00%
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	$ 33,021
Balance, end of year	$ 32,383	$ 33,021
Real assets
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Actual Allocation	3.00%	5.00%
Target allocation range, minimum	3.00%	3.00%
Target allocation range, maximum	10.00%	10.00%
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	$ 24,116
Balance, end of year	$ 13,622	$ 24,116
Private equity
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Actual Allocation	1.00%	1.00%
Target allocation range, minimum	0.00%	0.00%
Target allocation range, maximum	3.00%	3.00%
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	$ 3,682
Balance, end of year	$ 2,704	$ 3,682
Short-term Investments
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Actual Allocation	1.00%	2.00%
Target allocation range, minimum	0.00%	0.00%
Target allocation range, maximum	3.00%	3.00%
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	$ 8,044
Balance, end of year	4,564	$ 8,044
Quoted Prices in Active Markets for Identical Inputs (Level 1)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	318,044
Balance, end of year	313,830	318,044
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, beginning of year	17,092
Balance, end of year	18,908	17,092
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, beginning of year	18,006
Balance, end of year	24,652	18,006
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, beginning of year	946
Balance, end of year	1,410	946
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, beginning of year	43,710
Balance, end of year	46,594	43,710
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, beginning of year	128,033
Balance, end of year	131,109	128,033
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, beginning of year	52,674
Balance, end of year	42,720	52,674
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, beginning of year	29,799
Balance, end of year	22,393	29,799
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, beginning of year	27,784
Balance, end of year	26,044	27,784
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, beginning of year	0
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, beginning of year	0
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, beginning of year	0
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, beginning of year	0
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, beginning of year	98,900
Balance, end of year	84,719	98,900
Significant Other Observable Inputs (Level 2) | Corporate stocks
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	0
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, beginning of year	8,733
Balance, end of year	9,206	8,733
Significant Other Observable Inputs (Level 2) | Corporate stocks
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	0
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, beginning of year	0
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, beginning of year	0
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, beginning of year	0
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, beginning of year	74,525
Balance, end of year	70,949	74,525
Significant Other Observable Inputs (Level 2) | Foreign Corporate Debt Securities
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	0
Balance, end of year	0	0
Significant Other Observable Inputs (Level 2) | Absolute Return
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	0
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, beginning of year	7,598
Balance, end of year	0	7,598
Significant Other Observable Inputs (Level 2) | Private equity
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	0
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, beginning of year	8,044
Balance, end of year	4,564	8,044
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	53,221
Balance, end of year	48,709	53,221
Significant Unobservable Inputs (Level 3) | Corporate stocks
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	0
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, beginning of year	0
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, beginning of year	0
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, beginning of year	0
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, beginning of year	0
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, beginning of year	0
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, beginning of year	0
Balance, end of year	0	0
Significant Unobservable Inputs (Level 3) | Foreign Corporate Debt Securities
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	0
Balance, end of year	0	0
Significant Unobservable Inputs (Level 3) | Absolute Return
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	33,021
Balance, end of year	32,383	33,021
Significant Unobservable Inputs (Level 3) | Real assets
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	16,518
Balance, end of year	13,622	16,518
Significant Unobservable Inputs (Level 3) | Private equity
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	3,682
Balance, end of year	2,704	3,682
Significant Unobservable Inputs (Level 3) | Short-term Investments
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	0
Balance, end of year	0	0
Pension Benefits
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	25,607	22,205	$ 24,119
Interest cost	25,203	26,817	23,914
Expected return on plan assets	(28,297)	(26,624)	(23,909)
Net actuarial loss	20,028	17,639	26,371
Prior service cost (gain)	452	952	1,375
Settlement loss	0	789	0
Net periodic benefit cost	$ 42,993	$ 41,778	$ 51,870
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	4.08%	4.87%	3.95%
Expected return on plan assets	6.25%	6.25%	6.00%
Rate of compensation increase	4.47%	4.25%	4.25%
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
2016	$ 42,785
2017	41,056
2018	42,078
2019	44,673
2020	46,845
After 2020	245,255
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	470,165	$ 423,167
Realized gains	(13,283)	55,450
Balance, end of year	447,258	470,165	$ 423,167
Pension Benefits | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	53,221	57,978
Realized gains	1,045	510
Unrealized gains/(losses)	1,519	4,334
Purchases	460	407
Sales	(7,536)	(10,008)
Balance, end of year	48,709	53,221	57,978
Pension Benefits | Significant Unobservable Inputs (Level 3) | Absolute Return
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	33,021	39,448
Realized gains	108	386
Unrealized gains/(losses)	4	1,837
Purchases	272	0
Sales	(1,022)	(8,650)
Balance, end of year	32,383	33,021	39,448
Pension Benefits | Significant Unobservable Inputs (Level 3) | Real assets
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	16,518	14,737
Realized gains	763	48
Unrealized gains/(losses)	1,607	2,065
Purchases	0	48
Sales	(5,266)	(380)
Balance, end of year	13,622	16,518	14,737
Pension Benefits | Significant Unobservable Inputs (Level 3) | Private equity
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	3,682	3,793
Realized gains	174	76
Unrealized gains/(losses)	(92)	432
Purchases	188	359
Sales	(1,248)	(978)
Balance, end of year	2,704	3,682	3,793
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	2,505	2,454	2,644
Interest cost	2,925	3,338	2,873
Expected return on plan assets	0	0	0
Net actuarial loss	1,044	1,267	1,794
Prior service cost (gain)	(2,181)	(2,181)	(2,181)
Settlement loss	0	0	0
Net periodic benefit cost	$ 4,293	$ 4,878	$ 5,130
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	3.77%	4.34%	3.51%
Expected return on plan assets	0.00%	0.00%	0.00%
Rate of compensation increase	0.00%	0.00%	0.00%
Health care cost trend rate assumed for next fiscal year	6.50%
Ultimate health care cost trend rate	5.00%
Year that rate reaches ultimate trend rate	2019
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
2016	$ 5,748
2017	6,240
2018	6,552
2019	6,729
2020	6,909
After 2020	34,598
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Balance, beginning of year	0	$ 0
Realized gains	0	0
Balance, end of year	$ 0	$ 0	$ 0