Fair Value Part 3 (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities held to maturity	$ 1,178,440	$ 1,178,440		$ 1,170,685
Net LHFI	6,726,036	6,726,036		6,379,853
FDIC indemnification asset	1,749	1,749	$ 8,154	6,997	$ 14,347
Deposits	9,412,404	9,412,404		9,698,358
Long-term FHLB advances	1,173	1,173		1,253
Subordinated notes	49,961	49,961		49,936
Junior subordinated debt securities	61,856	61,856		61,856
Nonfinancial Assets and Liabilities [Abstract]
Outstanding balances in impaired loans	32,500	32,500		47,100
Foreclosed assets measured at fair value		26,800	30,000
Allowance for possible loan losses, Charge-offs for foreclosed assets upon initial recognition		7,400	9,300
Foreclosed assets re-measured after initial recognition		39,400	40,600
Write-downs of allowance for foreclosed assets after initial recognition		$ 2,400	$ 4,800
Estimated fair value of financial instruments with immediate and shorter-term maturities maximum		90 days
Noninterest gain Mortgage banking, net for changes in fair value of LHFS	3,600	$ 1,700
Interest earned on LHFS included in Interest and fees on LHFS and LHFI	1,400	3,700
Fair value and the contractual principal outstanding of the LHFS [Abstract]
Fair value of LHFS	146,621	146,621		91,182
LHFS contractual principal outstanding	141,366	141,366		88,106
Fair value less unpaid principal	5,255	5,255		3,076
Level 2 [Member] | Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and short-term investments	220,052	220,052		317,858
Securities held to maturity	1,178,440	1,178,440		1,170,685
Deposits	9,412,404	9,412,404		9,698,358
Short-term liabilities	1,244,049	1,244,049		868,620
Long-term FHLB advances	1,173	1,173		1,253
Subordinated notes	49,961	49,961		49,936
Junior subordinated debt securities	61,856	61,856		61,856
Level 2 [Member] | Estimate Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and short-term investments	220,052	220,052		317,858
Securities held to maturity	1,203,068	1,203,068		1,182,846
Deposits	9,416,869	9,416,869		9,702,864
Short-term liabilities	1,244,049	1,244,049		868,620
Long-term FHLB advances	1,179	1,179		1,263
Subordinated notes	52,027	52,027		53,504
Junior subordinated debt securities	50,759	50,759		46,392
Level 3 [Member] | Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net LHFI	6,726,036	6,726,036		6,379,853
Net acquired loans	406,988	406,988		537,350
FDIC indemnification asset	1,749	1,749		6,997
Level 3 [Member] | Estimate Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net LHFI	6,835,977	6,835,977		6,453,618
Net acquired loans	406,988	406,988		537,350
FDIC indemnification asset	$ 1,749	$ 1,749		$ 6,997