Other Comprehensive Income (Loss) - Components of accumulated other comprehensive income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 287,017
Other comprehensive income before reclassifications	(18,753)
Amounts reclassified from accumulated other comprehensive income	(38,701)	(27,511)
Net current period other comprehensive income (loss)	(57,454)	80,545
Ending balance	229,563
Unrealized gains on available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	289,957
Other comprehensive income before reclassifications	9,469
Amounts reclassified from accumulated other comprehensive income	(38,701)
Net current period other comprehensive income (loss)	(29,232)
Ending balance	260,725
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(2,940)
Other comprehensive income before reclassifications	(28,222)
Amounts reclassified from accumulated other comprehensive income	0
Net current period other comprehensive income (loss)	(28,222)
Ending balance	$ (31,162)