Fair Value Measurements and Disclosures (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Fair value adjustment of marketable securities and deferred compensation plan liability
Net gain on marketable securities	$ 397		$ 1,489		$ 723
Fair Value (Level 1) [Member]
Assets and Liabilities Reported at Fair Value
Marketable securities	$ 11,971	[1],[2]	$ 10,008	[1],[2]

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

[2] Fair value calculated using Level 1 inputs based on quoted prices in active markets for identical securities.