Fair Value Measurement (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Summary of marketable securities consist investments
Cost	$ 9,559	$ 8,735
Gross Unrealized Gains	27	22
Recorded Basis	18,987	16,748
Recorded Basis	11,276	9,899
Current Available-for-sale [Member]
Summary of marketable securities consist investments
Cost	18,954	16,728
Gross Unrealized Gains	33	20
Recorded Basis	18,987	16,748
Long-term Available-for-sale [Member]
Summary of marketable securities consist investments
Cost	11,262	9,870
Gross Unrealized Gains	14	29
Recorded Basis	11,276	9,899
Municipal bonds [Member]
Summary of marketable securities consist investments
Cost	5,107	4,920
Gross Unrealized Gains	22	17
Fair Value Category		2
Municipal bonds [Member] \| Current Available-for-sale [Member]
Summary of marketable securities consist investments
Cost	194	409
Gross Unrealized Gains	1	1
Recorded Basis	195	410
Fair Value Category		2
Municipal bonds [Member] \| Long-term Available-for-sale [Member]
Summary of marketable securities consist investments
Cost	1,938	292
Gross Unrealized Gains	3	1
Recorded Basis	1,941	293
Fair Value Category		2
Corporate bonds [Member]
Summary of marketable securities consist investments
Cost	2,360	2,035
Gross Unrealized Gains	5	5
Fair Value Category		2
Corporate bonds [Member] \| Current Available-for-sale [Member]
Summary of marketable securities consist investments
Cost	17,206	14,764
Gross Unrealized Gains	29	16
Recorded Basis	17,235	14,780
Fair Value Category		2
Corporate bonds [Member] \| Long-term Available-for-sale [Member]
Summary of marketable securities consist investments
Cost	8,854	9,111
Gross Unrealized Gains	11	28
Recorded Basis	8,865	9,139
Fair Value Category		2
Corporate bonds [Member] \| Held-to-maturity [Member]
Summary of marketable securities consist investments
Held-to-maturity, Cost	470	467
Held-to-maturity, Gross Unrealized Gains	0	0
Held-to-maturity, Recorded Basis	470	467
Fair Value Category		2
U.S. treasuries [Member]
Summary of marketable securities consist investments
Cost	2,092	1,780
Gross Unrealized Gains	0	0
Fair Value Category		1
U.S. treasuries [Member] \| Current Available-for-sale [Member]
Summary of marketable securities consist investments
Cost	1,554	1,555
Gross Unrealized Gains	3	3
Recorded Basis	1,557	1,558
Fair Value Category		$ 1

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Marketable securities unrealized holding gain loss.

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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