Organization and Basis of Presentation - Summary of Financial Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, carrying value	$ 152,263	$ 137,485
Marketable securities and other investments, amortized cost	144,808	130,335
Marketable securities and other investments, gross unrealized gain (loss)	7,455	7,150
Marketable securities	152,263	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)	347	68
Available-for-sale securities, carrying value	19,951	11,686
Investment Funds-U.S. Treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, amortized cost	7,600	3,675
Available-for-sale securities, gross unrealized gain (loss)	10	(9)
Available-for-sale securities, carrying value	7,610	3,666
Common Stock and Stock Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, amortized cost	29,970	34,655
Available-for-sale securities, gross unrealized gain (loss)	7,098	7,091
Available-for-sale securities, carrying value	37,068	41,746
Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, amortized cost	87,634	80,387
Held-to-maturity securities, gross unrealized gain (loss)	0	0
Held-to-maturity securities, carrying value	$ 87,634	$ 80,387