Securities Available-for-Sale (Details 1) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Maturity distribution of securities available-for-sale
Within one year, Amortized Cost	$ 69,122
After one but within five years, Amortized Cost	1,073,778
After five but within ten years, Amortized Cost	258,646
More than ten years, Amortized Cost	11,092
Nonmaturing, Amortized Cost	1,957
Total, Amortized Cost	1,414,595
Within one year, Fair Value	69,314
After one but within five years, Fair Value	1,091,554
After five but within ten years, Fair Value	261,371
More than ten years, Fair Value	10,539
Nonmaturing, Fair Value	2,023
Total, Fair Value	$ 1,434,801	$ 1,258,676