Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Premiums receivable, allowance for doubtful accounts	$ 1,671	$ 643
Preferred stock, par value (usd per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000us-gaap_PreferredStockSharesAuthorized	10,000,000us-gaap_PreferredStockSharesAuthorized
Preferred stock, shares issued	0us-gaap_PreferredStockSharesIssued	0us-gaap_PreferredStockSharesIssued
Preferred stock, shares outstanding	0us-gaap_PreferredStockSharesOutstanding	0us-gaap_PreferredStockSharesOutstanding
Common stock, par value (usd per share)	$ 0.001	$ 0.001
Common stock, shares authorized	350,000,000us-gaap_CommonStockSharesAuthorized	350,000,000us-gaap_CommonStockSharesAuthorized
Common stock, shares issued	152,451,000us-gaap_CommonStockSharesIssued	150,224,000us-gaap_CommonStockSharesIssued
Treasury stock, shares	74,378,000us-gaap_TreasuryStockShares	70,704,000us-gaap_TreasuryStockShares
Current [Member]
Investments available for sale, amortized cost	1,777,404	1,602,456
Noncurrent [Member]
Investments available for sale, amortized cost	$ 5,474	$ 67,943

A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

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