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Investments and Fair Value Measurements (Details) (USD $)
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3 Months Ended | 6 Months Ended | ||||||||||||
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Jun. 30, 2013
Investment
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Jun. 30, 2012
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Jun. 30, 2013
Investment
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Jun. 30, 2012
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Dec. 31, 2012
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| Schedule of Available-for-sale Securities [Line Items] | ||||||||||||||
| Amortized Cost | $ 52,679,000 | $ 52,679,000 | $ 34,264,000 | |||||||||||
| Unrealized Gains (Losses) | (555,000) | (555,000) | (269,000) | |||||||||||
| Aggregate Fair Value | 52,124,000 | 52,124,000 | 33,995,000 | |||||||||||
| Cash and cash equivalents | 50,000 | 50,000 | 1,150,000 | |||||||||||
| Short-term available-for-sale securities | 51,358,000 | 51,358,000 | 32,122,000 | |||||||||||
| Long-term available-for-sale securities | 716,000 | 716,000 | 723,000 | |||||||||||
| Aggregate fair value of short-term municipal bonds | 42,100,000 | 42,100,000 | 26,100,000 | |||||||||||
| Financial assets [Abstract] | ||||||||||||||
| ARS | 716,000 | 716,000 | 723,000 | |||||||||||
| Money market funds | 50,000 | 50,000 | 1,150,000 | |||||||||||
| Municipal securities | 51,358,000 | [1] | 51,358,000 | [1] | 32,122,000 | [1] | ||||||||
| Foreign currency exchange contracts | 36,000 | 36,000 | 952,000 | |||||||||||
| Total financial assets | 52,160,000 | 52,160,000 | 34,947,000 | |||||||||||
| Financial liabilities [Abstract] | ||||||||||||||
| Foreign currency exchange contracts | 447,000 | 447,000 | 115,000 | |||||||||||
| Total financial liabilities | 447,000 | 447,000 | 115,000 | |||||||||||
| Short-term municipal security funds as a percentage of municipal securities (in hundredths) | 82.00% | 82.00% | 82.00% | |||||||||||
| Municipal revenue bonds as a percentage of municipal securities (in hundredths) | 11.00% | 11.00% | 12.00% | |||||||||||
| Municipal general obligation bonds as a percentage of municipal securities (in hundredths) | 7.00% | 7.00% | 6.00% | |||||||||||
| Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] | ||||||||||||||
| Interest and dividend income | 160,000 | 618,000 | 287,000 | 859,000 | ||||||||||
| Reconciliation of available-for-sale ARS measured at fair value on a recurring basis using Level 3 inputs [Roll Forward] | ||||||||||||||
| Beginning balance | 729,000 | 703,000 | 723,000 | 700,000 | ||||||||||
| Total realized / unrealized losses [abstract] | ||||||||||||||
| Included in earnings | 0 | 0 | 0 | 0 | ||||||||||
| Included in OCI | (13,000) | 11,000 | (7,000) | 14,000 | ||||||||||
| Sales and settlements | 0 | 0 | 0 | 0 | ||||||||||
| Ending balance | 716,000 | 714,000 | 716,000 | 714,000 | ||||||||||
| Number of investments that failed at auction | 1 | 1 | ||||||||||||
| Principal amount of failed ARS auction | 1,000,000 | 1,000,000 | ||||||||||||
| Basis points (in hundredths) | 3.43% | 3.43% | ||||||||||||
| Valuation of Ars after discount has been applied | 700,000 | 700,000 | ||||||||||||
| Cost basis | 1,000,000 | 1,000,000 | ||||||||||||
| Accumulated Other Comprehensive Income, unrealized gains and losses on available for sale securities [Roll Forward] | ||||||||||||||
| Balance, January 1, | (180,000) | 135,000 | ||||||||||||
| Other comprehensive income, net of income taxes | (186,000) | (27,000) | ||||||||||||
| Balance, June 30, | (366,000) | 108,000 | (366,000) | 108,000 | ||||||||||
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Reclassification Out Of Accumulated Other Comprehensive Income [Member]
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| Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] | ||||||||||||||
| Interest and dividend income | 8,000 | 239,000 | 8,000 | 239,000 | ||||||||||
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Quoted Prices in Active Markets for Identical Assets (Level 1)
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| Financial assets [Abstract] | ||||||||||||||
| ARS | 0 | 0 | 0 | |||||||||||
| Money market funds | 50,000 | 50,000 | 1,150,000 | |||||||||||
| Municipal securities | 51,358,000 | [1] | 51,358,000 | [1] | 32,122,000 | [1] | ||||||||
| Foreign currency exchange contracts | 0 | 0 | 0 | |||||||||||
| Total financial assets | 51,408,000 | 51,408,000 | 33,272,000 | |||||||||||
| Financial liabilities [Abstract] | ||||||||||||||
| Foreign currency exchange contracts | 0 | 0 | 0 | |||||||||||
| Total financial liabilities | 0 | 0 | 0 | |||||||||||
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Significant Other Observable Inputs (Level 2) [Member]
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| Financial assets [Abstract] | ||||||||||||||
| ARS | 0 | 0 | 0 | |||||||||||
| Money market funds | 0 | 0 | 0 | |||||||||||
| Municipal securities | 0 | [1] | 0 | [1] | 0 | [1] | ||||||||
| Foreign currency exchange contracts | 36,000 | 36,000 | 952,000 | |||||||||||
| Total financial assets | 36,000 | 36,000 | 952,000 | |||||||||||
| Financial liabilities [Abstract] | ||||||||||||||
| Foreign currency exchange contracts | 447,000 | 447,000 | 115,000 | |||||||||||
| Total financial liabilities | 447,000 | 447,000 | 115,000 | |||||||||||
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Significant Other Unobservable Inputs (Level 3) [Member]
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| Financial assets [Abstract] | ||||||||||||||
| ARS | 716,000 | 716,000 | 723,000 | |||||||||||
| Money market funds | 0 | 0 | 0 | |||||||||||
| Municipal securities | 0 | [1] | 0 | [1] | 0 | [1] | ||||||||
| Foreign currency exchange contracts | 0 | 0 | 0 | |||||||||||
| Total financial assets | 716,000 | 716,000 | 723,000 | |||||||||||
| Financial liabilities [Abstract] | ||||||||||||||
| Foreign currency exchange contracts | 0 | 0 | 0 | |||||||||||
| Total financial liabilities | 0 | 0 | 0 | |||||||||||
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Auction Rate Securities ("ARS"), Greater Than One Year [Member]
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| Schedule of Available-for-sale Securities [Line Items] | ||||||||||||||
| Amortized Cost | 1,000,000 | 1,000,000 | 1,000,000 | |||||||||||
| Unrealized Gains (Losses) | (284,000) | (284,000) | (277,000) | |||||||||||
| Aggregate Fair Value | 716,000 | 716,000 | 723,000 | |||||||||||
| Cash and cash equivalents | 0 | 0 | 0 | |||||||||||
| Short-term available-for-sale securities | 0 | 0 | 0 | |||||||||||
| Long-term available-for-sale securities | 716,000 | 716,000 | 723,000 | |||||||||||
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Money Market Funds, Ninety Days or Less [Member]
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| Schedule of Available-for-sale Securities [Line Items] | ||||||||||||||
| Amortized Cost | 50,000 | 50,000 | 1,150,000 | |||||||||||
| Unrealized Gains (Losses) | 0 | 0 | 0 | |||||||||||
| Aggregate Fair Value | 50,000 | 50,000 | 1,150,000 | |||||||||||
| Cash and cash equivalents | 50,000 | 50,000 | 1,150,000 | |||||||||||
| Short-term available-for-sale securities | 0 | 0 | 0 | |||||||||||
| Long-term available-for-sale securities | 0 | 0 | 0 | |||||||||||
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Municipal Securities Maturing in One Year or Less [Member]
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| Schedule of Available-for-sale Securities [Line Items] | ||||||||||||||
| Amortized Cost | 43,093,000 | [2],[3] | 43,093,000 | [2],[3] | 26,885,000 | [2],[3] | ||||||||
| Unrealized Gains (Losses) | (109,000) | [2],[3] | (109,000) | [2],[3] | (1,000) | [2],[3] | ||||||||
| Aggregate Fair Value | 42,984,000 | [2],[3] | 42,984,000 | [2],[3] | 26,884,000 | [2],[3] | ||||||||
| Cash and cash equivalents | 0 | [2],[3] | 0 | [2],[3] | 0 | [2],[3] | ||||||||
| Short-term available-for-sale securities | 42,984,000 | [2],[3] | 42,984,000 | [2],[3] | 26,884,000 | [2],[3] | ||||||||
| Long-term available-for-sale securities | 0 | [2],[3] | 0 | [2],[3] | 0 | [2],[3] | ||||||||
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Municipal Securities Maturing After One Year Through Three Years [Member]
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| Schedule of Available-for-sale Securities [Line Items] | ||||||||||||||
| Amortized Cost | 2,517,000 | [2] | 2,517,000 | [2] | 1,345,000 | [2] | ||||||||
| Unrealized Gains (Losses) | 2,000 | [2] | 2,000 | [2] | 7,000 | [2] | ||||||||
| Aggregate Fair Value | 2,519,000 | [2] | 2,519,000 | [2] | 1,352,000 | [2] | ||||||||
| Cash and cash equivalents | 0 | [2] | 0 | [2] | 0 | [2] | ||||||||
| Short-term available-for-sale securities | 2,519,000 | [2] | 2,519,000 | [2] | 1,352,000 | [2] | ||||||||
| Long-term available-for-sale securities | 0 | [2] | 0 | [2] | 0 | [2] | ||||||||
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Municipal Securities Maturing Greater Than Three Years [Member]
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| Schedule of Available-for-sale Securities [Line Items] | ||||||||||||||
| Amortized Cost | 6,019,000 | [2] | 6,019,000 | [2] | 3,884,000 | [2] | ||||||||
| Unrealized Gains (Losses) | (164,000) | [2] | (164,000) | [2] | 2,000 | [2] | ||||||||
| Aggregate Fair Value | 5,855,000 | [2] | 5,855,000 | [2] | 3,886,000 | [2] | ||||||||
| Cash and cash equivalents | 0 | [2] | 0 | [2] | 0 | [2] | ||||||||
| Short-term available-for-sale securities | 5,855,000 | [2] | 5,855,000 | [2] | 3,886,000 | [2] | ||||||||
| Long-term available-for-sale securities | $ 0 | [2] | $ 0 | [2] | $ 0 | [2] | ||||||||
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