Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 25,574	$ 23,010	$ 20,507
Other comprehensive income (loss), net of taxes:
Cumulative translation adjustment	7,419	(1,335)	(2,682)
Changes in market value of investments:
Unrealized gain (loss), net of taxes of ($7), ($41) and ($513) for 2012, 2011 and 2010	14	(9)	(837)
Less: reclassification adjustment for net gains realized in net income, net of taxes of $12, $8 and $57 for 2012, 2011 and 2010	(17)	(12)	(88)
Net change in market value of investments	(3)	(21)	(925)
Other comprehensive income (loss)	7,416	(1,356)	(3,607)
Comprehensive income	$ 32,990	$ 21,654	$ 16,900