Income Taxes (Details 3) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Deferred tax assets:
Estimated claims incurred but not reported, a portion of which is deductible as paid for tax purposes	$ 5,160	$ 4,945
Vacation, bonus, stock compensation and other accruals, deductible as paid for tax purposes	28,273	27,182
Accounts receivable allowances, deductible as written off for tax purposes	9,614	7,532
Start-up costs, deductible in future periods for tax purposes	767	382
Unearned revenue, a portion of which is includible in income as received for tax purposes	0	8,257
2.0% Convertible Senior Notes	558	583
State net operating loss/credit carryforwards, deductible in future period for tax purpose	648	0
Gross deferred tax asset	45,020	48,881
Deferred tax liabilities:
Goodwill, due to timing differences in book and tax amortization	(6,529)	(5,500)
Unrealized gains on investments	(6,717)	(377)
Property, equipment and software, due to timing differences in book and tax depreciation	(24,075)	(20,060)
Deductible prepaid expenses and other	(2,426)	(2,274)
Gross deferred tax liabilities	(39,747)	(28,211)
Net deferred tax asset	$ 5,273	$ 20,670