Securities Available-for-Sale (Details 1) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Maturity distribution of securities available-for-sale
Within one year, Amortized Cost	$ 96,169
After one but within five years, amortized cost	925,961
After five but within ten years, amortized cost	173,923
More than 10 years, amortized cost	10,516
Non-maturing, amortized cost	1,958
Total, amortized cost	1,208,527
Within one year, fair value	96,670
After one but within five years, fair value	943,843
After five but within ten years, fair value	176,773
More than 10 years, fair value	9,776
Non-maturing, fair value	2,037
Total, fair value	$ 1,229,099	$ 1,258,676