Fair Value Information (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Interest Rate Swaps	$ 20,497	$ 9,127
Carrying Amount [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Interest Rate Swaps	20,497	9,127
Fair Value, Measurements, Recurring [Member] | Carrying Amount [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Assets	2,222,023	1,800,685
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Assets	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Assets	2,222,023	1,800,685
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Assets	0	0
Interest Rate Swaps [Member] | Fair Value, Measurements, Recurring [Member] | Carrying Amount [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Interest Rate Swaps	20,497	9,127
Interest Rate Swaps [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Interest Rate Swaps	0	0
Interest Rate Swaps [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Interest Rate Swaps	20,497	9,127
Interest Rate Swaps [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Interest Rate Swaps	0	0
Residential mortgage-backed securities[Member] | Fair Value, Measurements, Recurring [Member] | Carrying Amount [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	888,000	808,409
Residential mortgage-backed securities[Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	0	0
Residential mortgage-backed securities[Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	888,000	808,409
Residential mortgage-backed securities[Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	0	0
CMO's / REMIC's - Residential [Member] | Fair Value, Measurements, Recurring [Member] | Carrying Amount [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	604,508	270,477
CMO's / REMIC's - Residential [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	0	0
CMO's / REMIC's - Residential [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	604,508	270,477
CMO's / REMIC's - Residential [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	0	0
Government Agency [Member] | Fair Value, Measurements, Recurring [Member] | Carrying Amount [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	46,507	106,273
Government Agency [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	0	0
Government Agency [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	46,507	106,273
Government Agency [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	0	0
Municipal Bonds [Member] | Fair Value, Measurements, Recurring [Member] | Carrying Amount [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	652,037	606,399
Municipal Bonds [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	0	0
Municipal Bonds [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	652,037	606,399
Municipal Bonds [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	0	0
Other Securities [Member] | Fair Value, Measurements, Recurring [Member] | Carrying Amount [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	10,474
Other Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	0
Other Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	10,474
Other Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	0
Investment Securities [Member] | Fair Value, Measurements, Recurring [Member] | Carrying Amount [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	2,201,526	1,791,558
Investment Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	0	0
Investment Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	2,201,526	1,791,558
Investment Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Investment securities-AFS	0	0
Interest Rate Swaps [Member] | Fair Value, Measurements, Recurring [Member] | Carrying Amount [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Interest Rate Swaps	20,497	9,127
Interest Rate Swaps [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Interest Rate Swaps	0	0
Interest Rate Swaps [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Interest Rate Swaps	20,497	9,127
Interest Rate Swaps [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets and Liabilities Measured at Fair Value on a Recurring Basis
Interest Rate Swaps	$ 0	$ 0