Income Taxes (Tax Carryforwards) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Gross	$ 432,494	$ 547,890
Deferred Tax Assets, Valuation Allowance	(9,658)	(11,713)
Total deferred tax assets	422,836	$ 536,177
Federal [Member] | Net Operating Loss [Member] | 2031-2036 [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Gross	126,351
Deferred Tax Assets, Valuation Allowance	0
Total deferred tax assets	126,351
Pre-Tax Earnings Necessary to Realize	361,004
Federal [Member] | General Business Tax Credits [Member] | 2028-2036 [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Gross	8,383
Deferred Tax Assets, Valuation Allowance	0
Total deferred tax assets	8,383
Federal [Member] | Alternative Minimum Tax Credit [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Gross	43,037
Deferred Tax Assets, Valuation Allowance	0
Total deferred tax assets	43,037
State [Member] | Net Operating Loss [Member] | 2025-2029 [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Gross	13,244
Deferred Tax Assets, Valuation Allowance	0
Total deferred tax assets	13,244
Pre-Tax Earnings Necessary to Realize	1,370,624
State [Member] | Net Operating Loss [Member] | 2030-2036 [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Gross	36,148
Deferred Tax Assets, Valuation Allowance	0
Total deferred tax assets	36,148
Pre-Tax Earnings Necessary to Realize	1,165,627
State [Member] | Net Operating Loss [Member] | 2030-2036 [Member] | Global One [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Gross	3,000
State [Member] | Other Credits [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Gross	950
Deferred Tax Assets, Valuation Allowance	0
Total deferred tax assets	950
State [Member] | Other Credits [Member] | 2017-2020 [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Gross	12,422
Deferred Tax Assets, Valuation Allowance	(9,658)
Total deferred tax assets	2,764
State [Member] | Other Credits [Member] | 2021-2026 [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Gross	2,239
Deferred Tax Assets, Valuation Allowance	0
Total deferred tax assets	$ 2,239