Loans and Allowance for Loan Losses - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	$ 87,194	$ 70,204	$ 83,575	$ 67,240
Charged-off loans	(8,480)	(6,698)	(14,548)	(15,367)
Recovery of previously charged-off loans	4,344	2,762	6,847	7,464
Provision for loan losses	7,195	9,402	14,379	16,333
Ending Balance	90,253	75,670	90,253	75,670
Commercial real estate - mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	30,167	22,688	26,946	21,188
Charged-off loans	(1,065)	(234)	(1,599)	(962)
Recovery of previously charged-off loans	892	58	964	1,454
Provision for loan losses	832	2,336	4,515	3,168
Ending Balance	30,826	24,848	30,826	24,848
Consumer real estate - mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	8,369	5,100	7,670	5,031
Charged-off loans	(580)	(935)	(930)	(1,271)
Recovery of previously charged-off loans	372	537	741	1,203
Provision for loan losses	328	1,151	1,008	890
Ending Balance	8,489	5,853	8,489	5,853
Construction and land development
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	10,915	10,116	11,128	8,962
Charged-off loans	(4)	(10)	(4)	(12)
Recovery of previously charged-off loans	19	1,010	141	1,575
Provision for loan losses	276	(132)	(59)	459
Ending Balance	11,206	10,984	11,206	10,984
Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	32,699	26,648	31,731	24,863
Charged-off loans	(5,408)	(1,724)	(8,760)	(4,264)
Recovery of previously charged-off loans	2,744	567	4,342	1,455
Provision for loan losses	7,401	2,847	10,123	6,284
Ending Balance	37,436	28,338	37,436	28,338
Consumer and other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	4,803	5,476	5,423	5,874
Charged-off loans	(1,423)	(3,795)	(3,255)	(8,858)
Recovery of previously charged-off loans	317	590	659	1,777
Provision for loan losses	(1,583)	2,901	(713)	6,379
Ending Balance	2,114	5,172	2,114	5,172
Unallocated
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	241	176	677	1,322
Charged-off loans	0	0	0	0
Recovery of previously charged-off loans	0	0	0	0
Provision for loan losses	(59)	299	(495)	(847)
Ending Balance	$ 182	$ 475	$ 182	$ 475

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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