Fair Value Measurements (Details 1) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Available-for-sale Securities	$ 1,552,115	$ 1,494,745
Fair Value, Inputs, Level 1 [Member]
Available-for-sale Securities	516	507
Fair Value, Inputs, Level 2 [Member]
Available-for-sale Securities	1,515,077	1,456,334
Fair Value, Inputs, Level 3 [Member]
Available-for-sale Securities	36,522	37,904
Government agency and government-sponsored enterprise pass through securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	584,757
Government agency and government-sponsored enterprise pass through securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	0
Government agency and government-sponsored enterprise pass through securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	584,757
Government agency and government-sponsored enterprise pass through securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	0
Government agency and government-sponsored enterprise pass through securities | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	287,604
Government agency and government-sponsored enterprise pass through securities | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	0
Government agency and government-sponsored enterprise pass through securities | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	287,604
Government agency and government-sponsored enterprise pass through securities | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	0
Covered private label collateralized mortgage obligation [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	36,522
Covered private label collateralized mortgage obligation [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	0
Covered private label collateralized mortgage obligation [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	0
Covered private label collateralized mortgage obligation [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	36,522
Collateralized Mortgage Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	14,288
Collateralized Mortgage Obligations [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	0
Collateralized Mortgage Obligations [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	14,288
Collateralized Mortgage Obligations [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	0
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale Securities		436,658
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	456,566
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	0
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	456,566
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	0
Corporate Debt Securities [Member]
Available-for-sale Securities		82,707
Corporate Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	109,391
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	0
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	109,391
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	0
US Government-sponsored Enterprises Debt Securities [Member]
Available-for-sale Securities		9,872
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	36,665
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	0
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	36,665
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	0
Other securities [Member]
Available-for-sale Securities		27,543
Other securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	26,322
Other securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	516
Other securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	25,806
Other securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale Securities	$ 0