Income Taxes (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2035
Adjustment to Additional Paid in Capital, Income Tax Effect from Share-based Compensation, Net	$ 4,691	$ 1,096	$ (1,376)
DEFERRED TAX ASSETS:
Accrued liabilities	83,000	72,800
Accrued compensation and benefits	63,100	68,800
Net operating and capital loss carryforwards	20,800	21,600
Unrealized losses on investments	3,700	500
Insurance loss reserves and unearned premiums	15,400	13,700
Deferred gain in revenues	14,700	1,300
Tax Credits	5,500	10,800
Deferred tax assets before valuation alllowance	206,200	189,500
Valuation allowance	(22,400)	(13,300)
Net deferred tax assets	183,800	176,200
DEFERRED TAX LIABILITIES:
Depreciable and amortizable property	58,200	53,000
Prepaid expenses	11,300	10,700
Deferred revenue	5,200	9,600
Unrealized gains on investments	4,500	5,600
Other	1,400	6,300
Deferred tax liabilities	80,600	85,200
Additional Paid-in Capital [Member]
Operating Loss Carryforwards [Line Items]
Adjustment to Additional Paid in Capital, Income Tax Effect from Share-based Compensation, Net	$ 4,691	$ 1,096	$ (1,376)