CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest income:
Interest and fees on loans	$ 286,165	$ 253,949	$ 211,467
Interest and dividends on taxable investments	63,504	60,159	56,201
Interest and dividends on nontaxable investments	13,064	15,347	17,519
Total interest income	362,733	329,455	285,187
Interest expense:
Interest on deposits	10,658	8,031	7,325
Interest on borrowings	2,343	1,845	1,017
Interest on subordinated debt held by unconsolidated subsidiary trusts	4,677	3,904	2,949
Total interest expense	17,678	13,780	11,291
Net interest income	345,055	315,675	273,896
Provision for loan losses	10,837	10,984	8,076
Net interest income after provision for loan losses	334,218	304,691	265,820
Noninterest revenues:
Deposit service fees	70,384	67,896	58,595
Other banking revenues	4,968	5,466	7,477
Employee benefit services	92,279	80,830	46,628
Insurance services	30,317	26,150	23,149
Wealth management services	25,772	22,079	19,776
Unrealized gain on equity securities	657	0	0
Loss on debt extinguishment	(318)	0	0
Gain on sales of investment securities, net	0	2	0
Total noninterest revenues	224,059	202,423	155,625
Noninterest expenses:
Salaries and employee benefits	207,363	186,903	156,396
Occupancy and equipment	39,948	35,561	30,078
Data processing and communications	39,094	37,579	34,501
Amortization of intangible assets	18,155	16,941	5,479
Legal and professional fees	10,644	11,576	8,455
Business development and marketing	9,383	9,994	7,484
Acquisition expenses	(769)	25,986	1,706
Other expenses	21,471	22,609	22,749
Total noninterest expenses	345,289	347,149	266,848
Income before income taxes	212,988	159,965	154,597
Income taxes	44,347	9,248	50,785
Net income	$ 168,641	$ 150,717	$ 103,812
Basic earnings per share (in dollars per share)	$ 3.28	$ 3.07	$ 2.34
Diluted earnings per share (in dollars per share)	3.24	3.03	2.32
Cash dividends declared per share (in dollars per share)	$ 1.44	$ 1.32	$ 1.26