Loans and Leases (Details 10) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Sep. 30, 2018
Allowance for Loan and Lease Losses [Roll Forward]
Loans and Leases Receivable, Allowance, beginning balance	$ 132,472
Allowance for Loan and Lease Losses, Write-offs	(32,262)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	15,575
Allowance for Loan and Lease Losses Write-offs, Net	(16,687)
Provision for Loan and Lease Losses	23,000
Loans and Leases Receivable, Allowance, ending balance	138,785	$ 132,472
Loans held for investment, net	18,846,872	17,957,713
Non Purchased Credit Impaired Loans and Leases
Allowance for Loan and Lease Losses [Roll Forward]
Loans and Leases Receivable, Allowance, beginning balance	132,472	139,456	[1]
Allowance for Loan and Lease Losses, Write-offs	(32,262)	(59,042)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	15,575	15,284
Allowance for Loan and Lease Losses Write-offs, Net		(43,758)
Provision for Loan and Lease Losses	23,000	36,774
Loans and Leases Receivable, Allowance, ending balance	138,785	132,472
Financing Receivable, Individually Evaluated for Impairment	6,197			$ 4,031
Financing Receivable, Collectively Evaluated for Impairment	132,588			128,441
Financing Receivable, Individually Evaluated for Impairment	99,546			92,067
Financing Receivable, Collectively Evaluated for Impairment	18,747,326			17,865,646
Loans held for investment, net	18,846,872	17,957,713
Purchased Credit Impaired Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Loans and Leases Receivable, Allowance, Covered, beginning balance		6,400
Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for Loan and Lease Losses Write-offs, Net	(14)	(5,840)
Loans held for investment, net	7,972,747	7,918,141
Mortgages [Member] | Non Purchased Credit Impaired Loans and Leases
Allowance for Loan and Lease Losses [Roll Forward]
Loans and Leases Receivable, Allowance, beginning balance	46,021	40,051
Allowance for Loan and Lease Losses, Write-offs	(997)	(8,190)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	983	2,350
Provision for Loan and Lease Losses	(1,432)	11,810
Loans and Leases Receivable, Allowance, ending balance	44,575	46,021
Financing Receivable, Individually Evaluated for Impairment	231			417
Financing Receivable, Collectively Evaluated for Impairment	44,344			45,604
Financing Receivable, Individually Evaluated for Impairment	28,038			26,473
Financing Receivable, Collectively Evaluated for Impairment	7,944,709			7,891,668
Loans held for investment, net		7,918,141
Real Estate Construction [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for Loan and Lease Losses Write-offs, Net	0	195
Loans held for investment, net	2,737,802	2,233,656
Real Estate Construction [Member] | Non Purchased Credit Impaired Loans and Leases
Allowance for Loan and Lease Losses [Roll Forward]
Loans and Leases Receivable, Allowance, beginning balance	28,209	13,055
Allowance for Loan and Lease Losses, Write-offs	0	0
Allowance for Loan and Lease Loss, Recovery of Bad Debts	0	195
Provision for Loan and Lease Losses	2,335	14,959
Loans and Leases Receivable, Allowance, ending balance	30,544	28,209
Financing Receivable, Individually Evaluated for Impairment	0			0
Financing Receivable, Collectively Evaluated for Impairment	30,544			28,209
Financing Receivable, Individually Evaluated for Impairment	1,834			5,862
Financing Receivable, Collectively Evaluated for Impairment	2,735,968			2,227,794
Loans held for investment, net		2,233,656
Commercial Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for Loan and Lease Losses Write-offs, Net	(16,029)	(37,915)
Loans held for investment, net	7,695,496	7,404,595
Commercial Portfolio Segment [Member] | Non Purchased Credit Impaired Loans and Leases
Allowance for Loan and Lease Losses [Roll Forward]
Loans and Leases Receivable, Allowance, beginning balance	56,360	84,022
Allowance for Loan and Lease Losses, Write-offs	(30,426)	(50,481)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	14,397	12,566
Provision for Loan and Lease Losses	21,197	10,253
Loans and Leases Receivable, Allowance, ending balance	61,528	56,360
Financing Receivable, Individually Evaluated for Impairment	5,966			3,614
Financing Receivable, Collectively Evaluated for Impairment	55,562			52,746
Financing Receivable, Individually Evaluated for Impairment	69,674			59,288
Financing Receivable, Collectively Evaluated for Impairment	7,625,822			7,345,307
Loans held for investment, net		7,404,595
Consumer Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for Loan and Lease Losses Write-offs, Net	(644)	(198)
Loans held for investment, net	440,827	401,321
Consumer Portfolio Segment [Member] | Non Purchased Credit Impaired Loans and Leases
Allowance for Loan and Lease Losses [Roll Forward]
Loans and Leases Receivable, Allowance, beginning balance	1,882	2,328
Allowance for Loan and Lease Losses, Write-offs	(839)	(371)
Allowance for Loan and Lease Loss, Recovery of Bad Debts	195	173
Provision for Loan and Lease Losses	900	(248)
Loans and Leases Receivable, Allowance, ending balance	2,138	1,882
Financing Receivable, Individually Evaluated for Impairment	0			0
Financing Receivable, Collectively Evaluated for Impairment	2,138			1,882
Financing Receivable, Individually Evaluated for Impairment	0			444
Financing Receivable, Collectively Evaluated for Impairment	$ 440,827			$ 400,877
Loans held for investment, net		$ 401,321

[1] The allowance for loan losses related to PCI loans of $6.4 million as of December 31, 2017 is reflected in the beginning balance of the allowance for loan and lease losses for the year ended December 31, 2018.