SCHEDULE II VALUATION AND QUALIFYING ACCOUNTS (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Allowance for doubtful receivables
VALUATION AND QUALIFYING ACCOUNTS
Balance at the beginning of the period	$ 4,514	$ 3,778	$ 2,928
Additions, Charged to costs and expenses	2,223	2,303	2,146
Deductions from reserves	(1,912)	(1,567)	(1,296)
Balance at the end of the period	4,825	4,514	3,778
Deferred tax valuation allowance
VALUATION AND QUALIFYING ACCOUNTS
Balance at the beginning of the period	172	176	113
Additions, Charged to costs and expenses			63
Additions, Charged to other accounts		32
Deductions from reserves	(71)	(36)
Balance at the end of the period	$ 101	$ 172	$ 176