Fair Value Part 3 (Details) (USD $)	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity	$ 70,338,000		$ 42,188,000
Net LHFI	5,504,557,000		5,514,016,000
FDIC indemnification asset	17,342,000	25,309,000	21,774,000	28,348,000
Deposits	9,817,592,000		7,896,517,000
Long-term FHLB advances	8,679,000		0
Subordinated notes	49,888,000		49,871,000
Junior subordinated debt securities	61,856,000		61,856,000
Nonfinancial Assets and Liabilities [Abstract]
Outstanding balances in impaired loans	29,800,000		40,600,000
Foreclosed assets measured at fair value	60,500,000	16,600,000
Foreclosed assets measured at fair value, acquired	40,100,000	2,600,000
Allowance for possible loan losses, Charge-offs for foreclosed assets upon initial recognition	2,700,000	3,900,000
Foreclosed assets re-measured after initial recognition	28,300,000	21,300,000
Write-downs of allowance for foreclosed assets after initial recognition	4,400,000	4,100,000
Estimated fair value of financial instruments with immediate and shorter-term maturities maximum	90 days
Fair Value, Inputs, Level 2 [Member] | Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and short-term investments	309,401,000		238,535,000
Securities held to maturity	70,338,000		42,188,000
Deposits	9,817,592,000		7,896,517,000
Short-term liabilities	430,666,000		375,749,000
Long-term FHLB advances	8,679,000		0
Subordinated notes	49,888,000		49,871,000
Junior subordinated debt securities	61,856,000		61,856,000
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and short-term investments	309,401,000		238,535,000
Securities held to maturity	71,933,000		46,888,000
Deposits	9,825,081,000		7,904,179,000
Short-term liabilities	430,666,000		375,749,000
Long-term FHLB advances	8,679,000		0
Subordinated notes	53,509,000		53,980,000
Junior subordinated debt securities	40,206,000		40,206,000
Fair Value, Inputs, Level 3 [Member] | Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net LHFI	5,504,557,000		5,514,016,000
Net acquired loans	960,583,000		127,489,000
FDIC indemnification asset	17,342,000		21,774,000
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net LHFI	5,573,897,000		5,619,933,000
Net acquired loans	960,583,000		127,489,000
FDIC indemnification asset	$ 17,342,000		$ 21,774,000