Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
NET EARNINGS	$ 150,638	$ 120,371	$ 104,774
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	12,549	12,916	11,573
PROVISION FOR LOAN LOSSES	5,665	6,530	10,212
Securities premium amortization, net	27,467	30,310	29,005
Gain on sale of assets, net	(1,216)	(1,167)	(1,894)
Deferred federal income tax expense (benefit)	(250)	(53)	673
Change in loans held for sale	(5,791)	11,769	6,645
Change in other assets	(1,697)	9,313	2,397
Change in other liabilities	1,621	285	(2,643)
Total adjustments	38,348	69,903	55,968
Net cash provided by operating activities	188,986	190,274	160,742
CASH FLOWS FROM INVESTING ACTIVITIES:
Cash received in acquisition of Commercial Bancshares, Inc., net	18,653
Net decrease in interest-bearing time deposits in banks		249	1,788
Activity in available-for-sale securities:
Sales	220,259	120,576	40,510
Maturities	3,439,028	4,392,131	3,509,113
Purchases	(3,731,821)	(4,768,420)	(3,737,865)
Activity in held-to-maturity securities - maturities		124	157
Net increase in loans	(205,238)	(134,627)	(48,836)
Purchases of bank premises and equipment and other assets	(17,646)	(14,162)	(20,399)
Proceeds from sale of bank premises and equipment and other assets	844	6,085	3,572
Net cash used in investing activities	(275,921)	(398,044)	(251,960)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net increase (decrease) in noninterest-bearing deposits	(87,583)	323,928	(28,230)
Net increase (decrease) in interest-bearing deposits	(36,891)	160,494	316,600
Net increase (decrease) in borrowings	137,706	(114,770)	(169,905)
Common stock transactions:
Proceeds from stock issuances	3,864	2,934	1,260
Dividends paid	(53,861)	(48,955)	(44,907)
Net cash provided by (used in) financing activities	(36,765)	323,631	74,818
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(123,700)	115,861	(16,400)
CASH AND CASH EQUIVALENTS, beginning of year	372,347	256,486	272,886
CASH AND CASH EQUIVALENTS, end of year	$ 248,647	$ 372,347	$ 256,486