Employee Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Amounts recognized in the balance sheet, pre-tax:
Accumulated postretirement benefits obligation, current	$ (30,036)	$ (29,200)
Accumulated postretirement benefits obligation, long-term	(570,712)	(633,264)
Changes in plan assets and benefit obligations recognized in other comprehensive income (loss)
Current year net actuarial gain	130,867
Amortization of actuarial loss	28,545
Amortization of prior service cost	1,493
Total	160,905
Deferred income taxes	(60,013)	(23,330)	(33,179)
Total recognized in other comprehensive income (loss), net of taxes	(100,892)	40,501	53,224
Pension Benefits
Pension and Other Employee Benefits
Accumulated benefit obligation	247,874	278,357
Change in projected benefit obligation:
Benefit obligation at beginning of year	295,944	258,780
Service cost	7,062	5,991	5,163
Interest cost	12,280	12,517	12,576
Actuarial (gain) loss	(37,873)	29,933
Benefits paid	(11,763)	(11,501)
Plan amendments		224
Benefit obligation at end of year	265,650	295,944	258,780
Change in plan assets:
Fair value of plan assets at beginning of year	232,960	202,537
Actual return on plan assets	35,788	28,499
Employer contributions	780	13,425
Benefits paid	(11,763)	(11,501)
Fair value of plan assets at end of year	257,765	232,960	202,537
Unfunded status of the plan	(7,885)	(62,984)
Amounts recognized in the balance sheet, pre-tax:
Other long-term assets	1,260
Other current liabilities	(7,089)	(5,744)
Other long-term liabilities	(2,056)	(57,240)
Net amount recognized	(7,885)	(62,984)
Amounts recognized in accumulated other comprehensive income, pre-tax
Prior service cost	994	1,257
Net actuarial loss	48,331	114,787
Net amount recognized	49,325	116,044
Components of net periodic benefit cost:
Service cost	7,062	5,991	5,163
Interest cost	12,280	12,517	12,576
Expected return on plan assets	(16,941)	(16,125)	(15,717)
Amortization of prior service cost (credit)	263	256	272
Amortization of net actuarial loss	9,609	9,377	8,252
Settlement loss			1,807
Net periodic benefit cost	12,273	12,016	12,353
Estimated portion of net prior service cost and net actuarial loss remaining in accumulated other comprehensive income that is expected to be recognized as a component of net periodic benefit cost in 2014
Prior service cost	246
Net actuarial loss	2,566
Net amount to be recognized	2,812
Changes in plan assets and benefit obligations recognized in other comprehensive income (loss)
Current year net actuarial gain	56,721
Amortization of actuarial loss	9,609
Amortization of prior service cost	263
Total	66,593
Deferred income taxes	(24,986)
Total recognized in other comprehensive income (loss), net of taxes	41,607
Weighted average assumptions used to determine benefit obligations:
Discount rate (as a percent)	5.24%	4.29%	5.02%
Rate of compensation increase (as a percent)	3.70%	3.70%	3.70%
Weighted average assumptions used to determine net periodic cost:
Discount rate (as a percent)	4.29%	5.02%	5.30%
Expected return on plan assets (as a percent)	7.50%	7.75%	7.75%
Rate of compensation increase (as a percent)	3.70%	3.70%	3.70%
Other Postretirement Benefits
Pension and Other Employee Benefits
Accumulated benefit obligation	600,748	662,464
Change in projected benefit obligation:
Benefit obligation at beginning of year	662,464	577,918
Service cost	9,943	8,072	6,160
Interest cost	28,791	29,010	25,140
Actuarial (gain) loss	(74,146)	71,451
Benefits paid	(26,304)	(23,987)
Benefit obligation at end of year	600,748	662,464	577,918
Change in plan assets:
Employer contributions	26,304	23,987
Benefits paid	(26,304)	(23,987)
Unfunded status of the plan	(600,748)	(662,464)
Amounts recognized in the balance sheet, pre-tax:
Accumulated postretirement benefits obligation, current	(30,036)	(29,200)
Accumulated postretirement benefits obligation, long-term	(570,712)	(633,264)
Net amount recognized	(600,748)	(662,464)
Amounts recognized in accumulated other comprehensive income, pre-tax
Prior service cost	7,641	8,871
Net actuarial loss	238,693	331,775
Net amount recognized	246,334	340,646
Components of net periodic benefit cost:
Service cost	9,943	8,072	6,160
Interest cost	28,791	29,010	25,140
Amortization of prior service cost (credit)	1,230	1,045	(961)
Amortization of net actuarial loss	18,936	14,725	10,046
Net periodic benefit cost	58,900	52,852	40,385
Estimated portion of net prior service cost and net actuarial loss remaining in accumulated other comprehensive income that is expected to be recognized as a component of net periodic benefit cost in 2014
Prior service cost	1,227
Net actuarial loss	15,570
Net amount to be recognized	16,797
Changes in plan assets and benefit obligations recognized in other comprehensive income (loss)
Current year net actuarial gain	74,146
Amortization of actuarial loss	18,936
Amortization of prior service cost	1,230
Total	94,312
Deferred income taxes	(35,027)
Total recognized in other comprehensive income (loss), net of taxes	$ 59,285
Weighted average assumptions used to determine benefit obligations:
Discount rate (as a percent)	5.28%	4.44%	5.14%
Weighted average assumptions used to determine net periodic cost:
Discount rate (as a percent)	4.44%	5.14%	5.35%
Expected return on plan assets (as a percent)	7.25%