Securities (Details 3) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011
Contractual maturity of debt securities
Total	$ 575,034	$ 614,977	$ 580,059
Held for Investment [Member] | Estimated Market Value [Member]
Contractual maturity of debt securities
Within one year	1,602
After one year but within five years	14,909
After five years but within ten years	2,889
After ten years	704
Total	20,104
Held for Investment [Member] | Amortized Cost [Member]
Contractual maturity of debt securities
Within one year	1,583
After one year but within five years	14,679
After five years but within ten years	2,830
After ten years	642
Total	19,734
Available for Sale [Member] | Estimated Market Value [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Within one year	86,441
After one year but within five years	326,413
After five years but within ten years	49,031
After ten years	82,928
Total debt securities	544,813
Equity securities	10,487
Total	555,300
Available for Sale [Member] | Amortized Cost [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Within one year	85,373
After one year but within five years	323,771
After five years but within ten years	46,982
After ten years	80,458
Total debt securities	536,584
Equity securities	8,011
Total	$ 544,595