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Available-for-sale securities (Details) (USD $) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2014 | Mar. 31, 2013 | Dec. 31, 2013
Available-for-sale securities [Line Items] |  |  |
Investments used to satisfy obligations under nonqualified benefit plans | $ 63,300,000 | $ 53,300,000 | $ 62,400,000
Net unrealized gain (loss) of investments used to satify obligations under nonqualified benefit plans | 900,000 | 4,400,000 |
Available-for-sale securities [Abstract] |  |  |
Cost | 10,012,000 | 10,050,000 | 10,057,000
Gross unrealized gains | 72,000 | 172,000 | 84,000
Gross unrealized losses | (17,000) | (3,000) | (31,000)
Fair value | 10,067,000 | 10,219,000 | 10,110,000
Mortgage backed securities [Member] |  |  |
Available-for-sale securities [Abstract] |  |  |
Cost | 7,943,000 | 8,749,000 | 8,151,000
Gross unrealized gains | 63,000 | 133,000 | 69,000
Gross unrealized losses | (17,000) | (3,000) | (27,000)
Fair value | 7,989,000 | 8,879,000 | 8,193,000
US Treasury securities [Member] |  |  |
Available-for-sale securities [Abstract] |  |  |
Cost | 2,069,000 | 1,301,000 | 1,906,000
Gross unrealized gains | 9,000 | 39,000 | 15,000
Gross unrealized losses | 0 | 0 | (4,000)
Fair value | $ 2,078,000 | $ 1,340,000 | $ 1,917,000

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- Definition Investments used to satisfy obligations under unfunded, nonqualified benefit plans for executive officers and certain key management employees. + References No definition available. + Details
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- Definition Net unrealized gain (loss) of investments used to satisfy obligations under unfunded, nonqualified benefit plans for executive officers and certain key management employees. + References No definition available. + Details
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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 + Details
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- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + 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 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 + Details
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