Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Loan Portfolio Held for Investment (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Loan Portfolio [Abstract]
Total LHFI	$ 9,223,668	$ 8,835,868
Less allowance for loan losses, LHFI	83,226	79,290
Net LHFI	9,140,442	8,756,578
Construction, Land Development and Other Land [Member] \| Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total LHFI	1,135,999	1,056,601
Secured by 1-4 Family Residential Properties [Member] \| Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total LHFI	1,820,455	1,825,492
Other Real Estate Secured [Member] \| Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total LHFI	668,667	543,820
Secured by Nonfarm, Nonresidential Properties [Member] \| Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total LHFI	2,442,308	2,220,914
Commercial and Industrial Loans [Member]
Loan Portfolio [Abstract]
Total LHFI	1,491,367	1,538,715
Consumer Loans [Member]
Loan Portfolio [Abstract]
Total LHFI	176,894	182,448
State and Other Political Subdivision Loans [Member]
Loan Portfolio [Abstract]
Total LHFI	978,456	973,818
Other Loans [Member]
Loan Portfolio [Abstract]
Total LHFI	$ 509,522	$ 494,060

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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