Organization and Basis of Presentation - Summary of Financial Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, carrying value	$ 151,995	$ 139,189
Marketable securities and other investments, amortized cost	151,452	137,715
Marketable securities and other investments, gross unrealized gain (loss)	543	1,474
Marketable securities	151,995	139,189
Investment-Grade Unsecured Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, amortized cost	18,332	19,604
Available-for-sale securities, gross unrealized gain (loss)	148	(73)
Available-for-sale securities, carrying value	18,480	19,531
Investment Funds - U.S. Treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, amortized cost	7,774	10,022
Available-for-sale securities, gross unrealized gain (loss)	(23)	(22)
Available-for-sale securities, carrying value	7,751	10,000
Common Stock and Stock Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, amortized cost	23,663	13,696
Available-for-sale securities, gross unrealized gain (loss)	418	1,569
Available-for-sale securities, carrying value	24,081	15,265
Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, amortized cost	101,683	94,393
Held-to-maturity securities, gross unrealized gain (loss)	0	0
Held-to-maturity securities, carrying value	$ 101,683	$ 94,393

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