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Organization and Basis of Presentation - Summary of Financial Securities (Details) - USD ($) $ in Thousands | Sep. 30, 2016 | Dec. 31, 2015
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Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale securities, carrying value | $ 153,703 | $ 137,485
Marketable securities and other investments, amortized cost | 148,053 | 130,335
Marketable securities and other investments, gross unrealized gain (loss) | 5,650 | 7,150
Marketable securities | 153,703 | 137,485
Investment-Grade Unsecured Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale Securities, amortized cost | 19,604 | 11,618
Available-for-sale securities, gross unrealized gain (loss) | 416 | 68
Available-for-sale securities, carrying value | 20,020 | 11,686
Investment Funds-U.S. Treasuries [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale Securities, amortized cost | 7,598 | 3,675
Available-for-sale securities, gross unrealized gain (loss) | 2 | (9)
Available-for-sale securities, carrying value | 7,600 | 3,666
Common Stock and Stock Funds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale Securities, amortized cost | 29,901 | 34,655
Available-for-sale securities, gross unrealized gain (loss) | 5,232 | 7,091
Available-for-sale securities, carrying value | 35,133 | 41,746
Mortgage Backed Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Held-to-maturity Securities, amortized cost | 90,950 | 80,387
Held-to-maturity securities, gross unrealized gain (loss) | 0 | 0
Held-to-maturity securities, carrying value | $ 90,950 | $ 80,387

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