Condensed Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Statement of Other Comprehensive Income [Abstract]
Net income	$ 31,732	$ 48,074	$ 96,842	$ 162,845
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on available-for-sale securities, before tax	9,405	(118)	13,097	8,465
Income tax (expense) benefit related to unrealized gain (loss) on available-for-sale securities	(3,540)	45	(5,228)	(3,183)
Other comprehensive income (loss), net of tax	5,865	(73)	7,869	5,282
Comprehensive income	$ 37,597	$ 48,001	$ 104,711	$ 168,127