Organization and Basis of Presentation - Summary of Financial Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, carrying value	$ 153,703	$ 137,485
Marketable securities and other investments, amortized cost	148,053	130,335
Marketable securities and other investments, gross unrealized gain (loss)	5,650	7,150
Marketable securities	153,703	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)	416	68
Available-for-sale securities, carrying value	20,020	11,686
Investment Funds-U.S. Treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, amortized cost	7,598	3,675
Available-for-sale securities, gross unrealized gain (loss)	2	(9)
Available-for-sale securities, carrying value	7,600	3,666
Common Stock and Stock Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, amortized cost	29,901	34,655
Available-for-sale securities, gross unrealized gain (loss)	5,232	7,091
Available-for-sale securities, carrying value	35,133	41,746
Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, amortized cost	90,950	80,387
Held-to-maturity securities, gross unrealized gain (loss)	0	0
Held-to-maturity securities, carrying value	$ 90,950	$ 80,387