Income Taxes (Deferred Tax Assets and Liabilities) (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2034
Adjustment to Additional Paid in Capital, Income Tax Effect from Share-based Compensation, Net	$ 1,096,000	$ (1,376,000)	$ 5,130,000
DEFERRED TAX ASSETS:
Accrued liabilities	72,800,000	87,800,000
Accrued compensation and benefits	68,800,000	67,100,000
Net operating and capital loss carryforwards	21,600,000	22,200,000
Unrealized losses on investments	500,000us-gaap_DeferredTaxAssetsInvestments	16,700,000us-gaap_DeferredTaxAssetsInvestments
Insurance loss reserves and unearned premiums	13,700,000	12,700,000
Deferred gain in revenues	1,300,000us-gaap_DeferredTaxAssetsDeferredIncome	6,600,000us-gaap_DeferredTaxAssetsDeferredIncome
Tax Credits	10,800,000us-gaap_DeferredTaxAssetsOther	8,800,000us-gaap_DeferredTaxAssetsOther
Deferred tax assets before valuation alllowance	189,500,000us-gaap_DeferredTaxAssetsGross	221,900,000us-gaap_DeferredTaxAssetsGross
Valuation allowance	(13,300,000)	(23,300,000)
Net deferred tax assets	176,200,000us-gaap_DeferredTaxAssetsNet	198,600,000us-gaap_DeferredTaxAssetsNet
DEFERRED TAX LIABILITIES:
Depreciable and amortizable property	53,000,000	77,100,000
Prepaid expenses	10,700,000	14,900,000
Deferred revenue	9,600,000	13,200,000
Unrealized gains on investments	5,600,000	0
Other	6,300,000us-gaap_DeferredTaxLiabilitiesOther	4,000,000us-gaap_DeferredTaxLiabilitiesOther
Deferred tax liabilities	85,200,000us-gaap_DeferredTaxLiabilities	109,200,000us-gaap_DeferredTaxLiabilities
Capital Loss Carryforward [Member]
DEFERRED TAX ASSETS:
Net operating and capital loss carryforwards	6,000,000
Additional Paid-in Capital [Member]
Operating Loss Carryforwards [Line Items]
Adjustment to Additional Paid in Capital, Income Tax Effect from Share-based Compensation, Net	$ 1,096,000	$ (1,376,000)	$ 5,130,000

Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Insurance Loss Reserves and Unearned Premiums

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Deferred Tax Liabilities, Deferred Revenue

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Deferred Tax Liabilities, Unrealized Gains on Investments

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Amount of increase (decrease) in additional paid in capital (APIC) resulting from a tax benefit (deficiency) associated with an share-based compensation plan other than an employee stock ownership plan (ESOP).

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from deferred income.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences not separately disclosed.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from compensation and benefits costs.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from accrued liabilities.

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Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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Amount of deferred tax liability attributable to taxable temporary differences not separately disclosed.

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Amount of deferred tax consequences attributable to taxable temporary differences derived from prepaid expenses.

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Amount of deferred tax liability attributable to taxable temporary differences from property, plant, and equipment.

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Expiration date of each operating loss carryforward included in operating loss carryforward, in CCYY-MM-DD format.

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