Investment Securities (Roll Forward of Credit Losses of Held-to-Maturity Securities Written Down as Other-than-Temporary Impairment Recognized in Earnings and Other Comprehensive Income) (Details) (USD $) In Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2011	Jun. 30, 2010	Mar. 31, 2010
Investment Securities
Balance, beginning of period	$ 12,803	$ 12,778	$ 12,364	$ 12,653
Subsequent OTTI credit losses	47	72	289
Balance, end of period	$ 12,850	$ 12,850	$ 12,653	$ 12,653