CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Stockholders' equity:
Common stock, par value (in dollars per share)	0.001	0.001
Common stock, shares authorized (in shares)	300,000,000us-gaap_CommonStockSharesAuthorized	300,000,000us-gaap_CommonStockSharesAuthorized
Common stock, shares issued (in shares)	119,602,322us-gaap_CommonStockSharesIssued	118,442,726us-gaap_CommonStockSharesIssued
Common stock, shares outstanding (in shares)	119,602,322us-gaap_CommonStockSharesOutstanding	118,442,726us-gaap_CommonStockSharesOutstanding
1 Percent Convertible Senior Notes [Member]
LIABILITIES AND STOCKHOLDERS' EQUITY
Interest rate on convertible senior notes (in hundredths)	1.00%	1.00%
2 3/4 Percent Convertible Senior Notes [Member]
LIABILITIES AND STOCKHOLDERS' EQUITY
Interest rate on convertible senior notes (in hundredths)	2.75%	2.75%

Face amount or stated value per share of common stock.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Contractual interest rate for funds borrowed, under the debt agreement.

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