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Income taxes - Additional income tax details (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 30, 2013 | Dec. 31, 2013 | Dec. 31, 2015 | Dec. 31, 2014
Income Tax Disclosure [Abstract] |  |  |  |
Reduction in reserve for unrecognized tax benefits related to prior years |  | $ 14,300 |  |
Proceeds from income tax refunds | $ 5,009 |  |  |
Federal [Member] |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |
Operating loss carryforwards |  |  | $ 1,470,251 | $ 1,306,482
Accrued and Other Current Liabilities [Member] |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |
Income taxes payable |  |  | $ 13,092 | $ 14,302

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- Definition Carrying amount as of the balance sheet date of the unpaid sum of the known and estimated amounts payable to satisfy all currently due domestic and foreign income tax obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.20) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 15 -Article 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 15 -Subparagraph b(1) -Article 7 + Details
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- Definition Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319 + Details
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