Investments - Narrative (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) member	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 172,211,000		$ 172,211,000		$ 181,361,000
Number of Investment Committee Members Required to Authorize Investment | member			2
Debt securities	120,942,000		$ 120,942,000
Realized losses from the sale of available-for-sale securities (less than)	7,700,000	$ 0	10,900,000	$ 0
Proceeds from sales of available-for-sale securities			110,400,000	8,400,000
Maturities of investments			0	185,000,000
Unrealized losses	3,494,000		3,494,000		1,886,000
Other-than-temporary impairment loss	0	$ 0	366,000	$ 0
U.S. Treasury securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	24,923,000		24,923,000
Unrealized losses	7,000		7,000
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Fair Value	96,019,000		96,019,000		139,132,000
Debt securities	96,000,000		96,000,000
Unrealized losses	2,257,000		2,257,000		1,769,000
Preferred stock
Schedule of Available-for-sale Securities [Line Items]
Fair Value	40,277,000		40,277,000		36,593,000
Preferred stock investments	40,300,000		40,300,000
Unrealized losses	1,103,000		1,103,000		$ 111,000
Common stock
Schedule of Available-for-sale Securities [Line Items]
Fair Value	6,523,000		6,523,000
Preferred stock investments	6,500,000		6,500,000
Unrealized losses	123,000		123,000
Sears Holdings Corp or affiliates | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Debt securities	8,600,000		8,600,000
Sears Holdings Corp or affiliates | Preferred stock
Schedule of Available-for-sale Securities [Line Items]
Preferred stock investments	$ 100,000		$ 100,000
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	35.43%		35.43%