Investments - Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) member	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 149,698,000		$ 149,698,000		$ 181,361,000
Number of Investment Committee Members Required to Authorize Investment | member			2
Debt securities	111,503,000		$ 111,503,000
Available-for-sale securities, gross realized gain (loss)	(100,000)	$ 100,000	10,800,000	$ 100,000
Proceeds from sales of available-for-sale securities			144,300,000	83,300,000
Maturities of investments			0	185,000,000
Unrealized losses	3,420,000		3,420,000		1,886,000
Other-than-temporary impairment loss	403,000	$ 0	769,000	$ 0
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	9,996,000		9,996,000
Unrealized losses	0		0
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	101,507,000		101,507,000		139,132,000
Debt securities	101,500,000		101,500,000
Unrealized losses	2,522,000		2,522,000		1,769,000
Preferred stock
Schedule of Available-for-sale Securities [Line Items]
Fair Value	33,733,000		33,733,000		36,593,000
Preferred stock investments	33,700,000		33,700,000
Unrealized losses	898,000		898,000		$ 111,000
Sears Holdings Corp or affiliates | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Debt securities	9,200,000		9,200,000
Sears Holdings Corp or affiliates | Preferred stock
Schedule of Available-for-sale Securities [Line Items]
Preferred stock investments	$ 200,000		$ 200,000
Required percent of investment account held in cash or cash equivalents | Minimum
Schedule of Available-for-sale Securities [Line Items]
Investments, target portfolio allocations			25.00%
Other aggregated investments | Minimum | Securities of any one issuer (excluding the U.S. Government)
Schedule of Available-for-sale Securities [Line Items]
Investments, portfolio allocations requiring additional consent			10.00%
Other aggregated investments | Maximum | Securities of any one issuer (excluding the U.S. Government)
Schedule of Available-for-sale Securities [Line Items]
Investments, target portfolio allocations			15.00%
Investments, portfolio allocations requiring additional consent			15.00%
Other aggregated investments | Maximum | Single Issuer, exchange-traded common equities
Schedule of Available-for-sale Securities [Line Items]
Investments, target portfolio allocations			5.00%
Common stock investments | Maximum
Schedule of Available-for-sale Securities [Line Items]
Investments, target portfolio allocations, amount			$ 100,000,000.0
Common, preferred or other equity investments | Maximum
Schedule of Available-for-sale Securities [Line Items]
Investments, target portfolio allocations			25.00%
Investor | Fairholme Capital Management, L.L.C.
Schedule of Available-for-sale Securities [Line Items]
Common stock ownership percentage	40.58%		40.58%