Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net Income	$ 57,957	$ 64,072	$ 52,695
Other Comprehensive Income:
Unrealized gains on investments in marketable securities	23,099	598	15,016
Income tax expense related to items of other comprehensive income	(8,993)	(183)	(5,809)
Other comprehensive income, net of tax	14,106	415	9,207
Comprehensive Income	$ 72,063	$ 64,487	$ 61,902