CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest income:
Interest and fees on loans	$ 314,779	$ 308,210	$ 286,165
Interest and dividends on taxable investments	62,538	65,904	63,504
Interest and dividends on nontaxable investments	11,961	11,613	13,064
Total interest income	389,278	385,727	362,733
Interest expense:
Interest on deposits	16,761	20,460	10,658
Interest on borrowings	1,569	1,848	2,343
Interest on subordinated notes payable	670	346	0
Interest on subordinated debt held by unconsolidated subsidiary trusts	1,875	3,898	4,677
Total interest expense	20,875	26,552	17,678
Net interest income	368,403	359,175	345,055
Provision for credit losses	14,212	8,430	10,837
Net interest income after provision for credit losses	354,191	350,745	334,218
Noninterest revenues:
Deposit service fees	57,370	65,602	70,384
Mortgage banking	5,301	523	1,400
Other banking services	3,753	4,358	3,568
Employee benefit services	101,329	97,167	92,279
Insurance services	32,372	32,199	30,317
Wealth management services	27,879	25,869	25,772
Unrealized (loss) gain on equity securities	(6)	19	657
Gain (loss) on debt extinguishment	421	0	(318)
Gain on sales of investment securities, net	0	4,882	0
Total noninterest revenues	228,419	230,619	224,059
Expenses:
Salaries and employee benefits	228,384	219,916	207,363
Occupancy and equipment	40,732	39,850	39,948
Data processing and communications	45,755	41,407	39,094
Amortization of intangible assets	14,297	15,956	18,155
Legal and professional fees	11,605	10,783	10,644
Business development and marketing	9,463	11,416	9,383
Litigation accrual	2,950	0	0
Acquisition expenses	4,933	8,608	(769)
Other expenses	18,415	24,090	21,471
Total noninterest expenses	376,534	372,026	345,289
Income before income taxes	206,076	209,338	212,988
Income taxes	41,400	40,275	44,347
Net income	$ 164,676	$ 169,063	$ 168,641
Basic earnings per share (in dollars per share)	$ 3.10	$ 3.26	$ 3.28
Diluted earnings per share (in dollars per share)	$ 3.08	$ 3.23	$ 3.24