Loans and Allowance for Credit Losses - Schedule of Amortized Cost and Unpaid Principal for Impaired Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 4,852,911		$ 4,194,512
Unpaid Principal	4,878,269		4,209,477
Difference	(25,358)		(14,965)
Allowance for credit losses	(90,995)	$ (54,613)	(29,092)	$ (31,895)	$ (29,416)	$ (27,571)
Loans, net	4,761,916		4,165,420
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	762,531		1,046,961
Unpaid Principal	766,471		1,051,684
Difference	(3,940)		(4,723)
Allowance for credit losses	(13,152)	(15,539)	(5,353)	(5,798)	(5,677)	(4,493)
Construction, land development, land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	244,512		160,569
Unpaid Principal	244,966		162,335
Difference	(454)		(1,766)
Allowance for credit losses	(5,600)	(5,917)	(1,382)	(1,084)	(1,035)	(1,134)
1-4 family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	164,785		179,425
Unpaid Principal	165,442		180,340
Difference	(657)		(915)
Allowance for credit losses	(1,972)	(2,027)	(308)	(417)	(409)	(317)
Farmland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	110,966		154,975
Unpaid Principal	111,870		156,995
Difference	(904)		(2,020)
Allowance for credit losses	(863)	(958)	(670)	(939)	(590)	(535)
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,536,903		1,342,683
Unpaid Principal	1,554,805		1,346,444
Difference	(17,902)		(3,761)
Allowance for credit losses	(22,713)	(23,283)	(12,566)	(14,771)	(13,899)	(12,865)
Factored receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	1,016,337		619,986
Unpaid Principal	1,017,805		621,697
Difference	(1,468)		(1,711)
Allowance for credit losses	(44,985)	(5,244)	(7,657)	(7,717)	(6,861)	(7,299)
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	17,106		21,925
Unpaid Principal	17,139		21,994
Difference	(33)		(69)
Allowance for credit losses	(710)	(768)	(488)	(581)	(563)	(615)
Mortgage warehouse
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	999,771		667,988
Unpaid Principal	999,771		667,988
Difference	0		0
Allowance for credit losses	$ (1,000)	$ (877)	$ (668)	$ (588)	$ (382)	$ (313)