Fair Value Part 3 (Details) (USD $)	9 Months Ended
	Sep. 30, 2013	Sep. 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	$ 69,980,000		$ 42,188,000
Net LHFI	5,628,009,000		5,514,016,000
FDIC indemnification asset	17,085,000	23,979,000	21,774,000	28,348,000
Deposits	9,787,234,000		7,896,517,000
Long-term FHLB advances	8,562,000		0
Subordinated notes	49,896,000		49,871,000
Junior subordinated debt securities	61,856,000		61,856,000
Nonfinancial Assets and Liabilities [Abstract]
Outstanding balances in impaired loans	32,200,000		40,600,000
Foreclosed assets measured at fair value	73,900,000	32,400,000
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	9,200,000	8,500,000
Foreclosed assets re-measured after initial recognition	35,000,000	29,700,000
Write-downs of allowance for foreclosed assets after initial recognition	5,500,000	4,800,000
Estimated fair value of financial instruments with immediate and shorter-term maturities maximum	90 days
Level 2 [Member] | Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and short-term investments	343,562,000		238,535,000
Securities held to maturity	69,980,000		42,188,000
Deposits	9,787,234,000		7,896,517,000
Short-term liabilities	403,163,000		375,749,000
Long-term FHLB advances	8,562,000		0
Subordinated notes	49,896,000		49,871,000
Junior subordinated debt securities	61,856,000		61,856,000
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	343,562,000		238,535,000
Securities held to maturity	70,949,000		46,888,000
Deposits	9,792,076,000		7,904,179,000
Short-term liabilities	403,163,000		375,749,000
Long-term FHLB advances	8,562,000		0
Subordinated notes	53,605,000		53,980,000
Junior subordinated debt securities	40,206,000		40,206,000
Level 3 [Member] | Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net LHFI	5,628,009,000		5,514,016,000
Net acquired loans	869,792,000		127,489,000
FDIC indemnification asset	17,085,000		21,774,000
Level 3 [Member] | Estimate of Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net LHFI	5,701,646,000		5,619,933,000
Net acquired loans	869,792,000		127,489,000
FDIC indemnification asset	$ 17,085,000		$ 21,774,000