Securities (Securities, With Unrealized Losses Segregated By Length Of Impairment) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available for Sale, Less than 12 months, Estimated Fair Value	$ 252,573
Available for Sale, More than 12 Months, Estimated Fair Value	49
Available for Sale, Total, Estimated Fair Value	252,622
Available for Sale, Less than 12 Months, Unrealized Losses	246
Available for Sale, More than 12 Months, Unrealized Losses	1
Available for Sale, Total, Unrealized Losses	247
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for Sale, Less than 12 months, Estimated Fair Value	250,332
Available for Sale, More than 12 Months, Estimated Fair Value
Available for Sale, Total, Estimated Fair Value	250,332
Available for Sale, Less than 12 Months, Unrealized Losses	219
Available for Sale, More than 12 Months, Unrealized Losses
Available for Sale, Total, Unrealized Losses	219
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for Sale, Less than 12 months, Estimated Fair Value	16
Available for Sale, More than 12 Months, Estimated Fair Value	49
Available for Sale, Total, Estimated Fair Value	65
Available for Sale, More than 12 Months, Unrealized Losses	1
Available for Sale, Total, Unrealized Losses	1
States And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for Sale, Less than 12 months, Estimated Fair Value	2,225
Available for Sale, Total, Estimated Fair Value	2,225
Available for Sale, Less than 12 Months, Unrealized Losses	27
Available for Sale, Total, Unrealized Losses	$ 27