Accumulated Other Comprehensive Income (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2012
Reclassifications From Accumulated Other Comprehensive Income
Interest and other income (expense), net	$ (2,977)	$ (130)		$ (4,610)	$ (1,105)
Provision for income taxes	(4,561)	(4,812)		(5,390)	(13,181)
Net income	9,813	7,698		17,803	22,434
Transfers out of accumulated other comprehensive income			0
Reclassifications from accumulated other comprehensive income
Reclassifications From Accumulated Other Comprehensive Income
Net income				11
Realized gain on sale of marketable securities | Reclassifications from accumulated other comprehensive income
Reclassifications From Accumulated Other Comprehensive Income
Interest and other income (expense), net				19
Income tax benefit | Reclassifications from accumulated other comprehensive income
Reclassifications From Accumulated Other Comprehensive Income
Provision for income taxes				$ (8)