Fair Value Measurements and Disclosures (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012	Dec. 31, 2012
Assets and Liabilities Reported at Fair Value
Marketable securities	$ 8,029			$ 7,435
Fair value adjustment of marketable securities and deferred compensation plan liability
Net gain (loss) on marketable securities	356		435
Fair Value (Level 1) [Member]
Assets and Liabilities Reported at Fair Value
Marketable securities	$ 8,029	[1],[2]		$ 7,435	[1],[2]

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

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