Investments and Notes Receivable - Investments and Other Receivables Summary (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment Holdings [Line Items]
Investments and notes receivable	$ 240,538	$ 254,144
Available-for-sale investments [Member]
Investment Holdings [Line Items]
Securities in continuous loss position less than 12 months	12,300
Investments [Member]
Investment Holdings [Line Items]
Fair value	80,902	106,593
Investments [Member] \| Available-for-sale investments [Member]
Investment Holdings [Line Items]
Amortized cost	73,573	98,980
Gross unrealized gains	7,354	8,210
Gross unrealized losses	(25)	(702)
Fair value	80,902	106,488
Investments [Member] \| Available-for-sale investments [Member] \| Student Loan Asset-Backed and Other Debt Securities [Member]
Investment Holdings [Line Items]
Amortized cost	71,943	98,260
Gross unrealized gains	5,056	6,280
Gross unrealized losses	(25)	(641)
Fair value	76,974	103,899
Investments [Member] \| Available-for-sale investments [Member] \| Equity securities [Member]
Investment Holdings [Line Items]
Amortized cost	1,630	720
Gross unrealized gains	2,298	1,930
Gross unrealized losses	0	(61)
Fair value	3,928	2,589
Investments [Member] \| Trading investments [Member] \| Equity securities [Member]
Investment Holdings [Line Items]
Fair value	0	105
Miscellaneous Investments [Member] \| Venture Capital Funds [Member]
Investment Holdings [Line Items]
Other investments	84,752	69,789
Miscellaneous Investments [Member] \| Real Estate Investment [Member]
Investment Holdings [Line Items]
Other investments	49,464	48,379
Miscellaneous Investments [Member] \| Notes Receivable [Member]
Investment Holdings [Line Items]
Other investments	16,393	17,031
Miscellaneous Investments [Member] \| Tax liens and affordable housing investments [Member]
Investment Holdings [Line Items]
Other investments	$ 9,027	$ 12,352

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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