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Convertible Securities (Details) $ / shares in Units, shares in Millions | 12 Months Ended
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Dec. 31, 2015 USD ($) trading_day $ / shares | Dec. 31, 2014 USD ($) shares
Debt Instrument |  |
Shares issued in conversion | shares |  | 1.9
Loss recognized on conversion of debt securities |  | $ 18,800,000
2006 Junior Convertible Securities |  |
Debt Instrument |  |
Outstanding principal of junior convertible trust preferred securities |  | $ 300,000,000.0
2007 Junior Convertible Securities |  |
Debt Instrument |  |
Stated interest rate | 5.15% |
Principal amount at maturity | $ 50 |
Conversion ratio (in shares) | 0.25 |
Conversion price (in usd per share) | $ / shares | $ 200 |
Redemption closing price trigger | $ / shares | $ 260 |
Number of trading days closing price has exceeded threshold | trading_day | 20 |
Consecutive trading days | 30 days |
Deferred tax liability | $ 9,400,000 |
Common Stock |  |
Debt Instrument |  |
Shares issued in conversion | shares |  | 1.9

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- Definition Represents the deferred taxes generated from the excess of the interest expense calculated under federal income tax regulations over interest expense as calculated for book purposes. + References No definition available. + Details
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- Definition Gain (Loss) on Conversion of Debt Securities + References No definition available. + Details
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- Definition The amount of the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586 + Details
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- Definition The price per share of the conversion feature embedded in the debt instrument. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6928298&loc=SL6031898-161870 + Details
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- Definition Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21506-112644 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Conversion Rate -URI http://asc.fasb.org/extlink&oid=6509012 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(5)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21521-112644 + Details
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- Definition Threshold period of specified consecutive trading days within which common stock price to conversion price of convertible debt instruments must exceed threshold percentage for a specified number of trading days to trigger conversion feature, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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