Fair Value Measurements and Disclosures (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Fair value adjustment of marketable securities and deferred compensation plan liability
Net gain on marketable securities		$ (681)	$ (39)	$ (171)	$ 507
Trading Securities		12,638		12,638		$ 11,971
Fair Value (Level 1) [Member]
Assets and Liabilities Reported at Fair Value
Marketable securities	[1],[2]	$ 12,638		$ 12,638		$ 11,971

[1] Based on quoted prices in active markets for identical securities.

[2] The marketable securities are held in a limited rabbi trust.