Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] |
| | Fair Value Measurements Using | | September 30, 2018 | | Fair Value | | | Quoted Prices in Active Markets For Identical Assets (Level 1) | | | Significant Other Observable Inputs (Level 2) | | | Significant Unobservable Inputs (Level 3) | | Cash and cash equivalents | | $ | 55,599 | | | $ | 55,599 | | | $ | – | | | $ | – | | Restricted cash and cash equivalents | | | 12,134 | | | | 12,134 | | | | – | | | | – | | Marketable equity securities | | | 139,502 | | | | 139,502 | | | | – | | | | – | | Corporate debt securities | | | 66,190 | | | | 43,901 | | | | 22,289 | | | | – | | Mortgage–backed securities | | | 56,293 | | | | – | | | | 56,293 | | | | – | | U.S. Treasury securities | | | 22,540 | | | | 22,540 | | | | – | | | | – | | State and municipal securities | | | 23,011 | | | | – | | | | 23,011 | | | | – | | Total financial assets | | $ | 375,269 | | | $ | 273,676 | | | $ | 101,593 | | | $ | – | | | | Fair Value Measurements Using | | December 31, 2017 | | Fair Value | | | Quoted Prices in Active Markets For Identical Assets (Level 1) | | | Significant Other Observable Inputs (Level 2) | | | Significant Unobservable Inputs (Level 3) | | Cash and cash equivalents | | $ | 59,118 | | | $ | 59,118 | | | $ | – | | | $ | – | | Restricted cash and cash equivalents | | | 8,303 | | | | 8,303 | | | | – | | | | – | | Marketable equity securities | | | 139,085 | | | | 139,085 | | | | – | | | | – | | Corporate debt securities | | | 65,461 | | | | 43,073 | | | | 22,388 | | | | – | | Mortgage-backed securities | | | 53,544 | | | | – | | | | 53,544 | | | | – | | U.S. Treasury securities | | | 21,172 | | | | 21,172 | | | | – | | | | – | | State and municipal securities | | | 26,218 | | | | – | | | | 26,218 | | | | – | | Total financial assets | | $ | 372,901 | | | $ | 270,751 | | | $ | 102,150 | | | $ | – | |
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