Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 2,435	$ 10,710	$ 10,789	$ 21,418
Other comprehensive income, net of taxes:
Cumulative translation adjustments	1,560	7,197	221	6,865
Changes in market value of investments:
Unrealized gain (loss), net of taxes (benefits) of $143 and $188 for the three months ended September 30, 2013 and 2012, and $(98) and $354 for the nine months ended September 30, 2013 and 2012	238	291	(202)	624
Less: reclassification adjustment for net (gains) losses realized in net income, net of taxes of $4 and $2 for the three months ended September 30, 2013 and 2012, and $(11) and $12 for the nine months ended September 30, 2013 and 2012	(7)	(3)	17	(17)
Net change in market value of investments	231	288	(185)	607
Other comprehensive income	1,791	7,485	36	7,472
Comprehensive income	$ 4,226	$ 18,195	$ 10,825	$ 28,890