Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Components of accumulated other comprehensive income, included in stockholders' equity
Unrealized gains on available-for-sale securities	$ 39,539	$ 95,328
Tax effect	(15,381)	(37,083)
Net of tax amount	24,158	58,245
Unrealized losses on derivatives used for cash flow hedges	(1,270)	(16,832)
Tax effect	494	6,549
Net of tax amount	(776)	(10,283)
Total accumulated other comprehensive income	$ 23,382	$ 47,962