Securities Available-for-Sale (Details 1) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Maturity distribution of securities available-for-sale
Within one year, Amortized Cost	$ 64,221
After one but within five years, Amortized Cost	1,021,035
After five but within ten years, Amortized Cost	293,758
More than 10 years, Amortized Cost	11,221
Non-maturing, Amortized Cost	1,958
Total, Amortized Cost	1,392,193
Within one year, Fair Value	64,403
After one but within five years, Fair Value	1,035,071
After five but within ten years, Fair Value	295,090
More than 10 years, Fair Value	10,675
Non-maturing, Fair Value	2,021
Total, Fair Value	$ 1,407,260	$ 1,434,801