CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest income:
Interest and fees on loans	$ 253,949	$ 211,467	$ 187,743
Interest and dividends on taxable investments	60,159	56,201	52,871
Interest and dividends on nontaxable investments	15,347	17,519	19,008
Total interest income	329,455	285,187	259,622
Interest expense:
Interest on deposits	8,031	7,325	6,971
Interest on borrowings	1,845	1,017	1,694
Interest on subordinated debt held by unconsolidated subsidiary trusts	3,904	2,949	2,537
Total interest expense	13,780	11,291	11,202
Net interest income	315,675	273,896	248,420
Provision for loan losses	10,984	8,076	6,447
Net interest income after provision for loan losses	304,691	265,820	241,973
Noninterest revenues:
Deposit service fees	67,896	58,595	52,747
Other banking revenues	5,466	7,477	4,960
Employee benefit services	80,830	46,628	45,388
Insurance services	26,150	23,149	3,352
Wealth management services	22,079	19,776	16,856
Gain/(loss) on sales of investment securities, net	2	0	(4)
Total noninterest revenues	202,423	155,625	123,299
Noninterest expenses:
Salaries and employee benefits	179,993	151,647	126,356
Occupancy and equipment	35,561	30,078	27,593
Data processing and communications	37,579	34,501	30,430
Amortization of intangible assets	16,941	5,479	3,663
Legal and professional fees	11,576	8,455	6,813
Office supplies and postage	7,506	7,274	6,476
Business development and marketing	9,994	7,484	7,204
FDIC insurance premiums	3,473	3,671	3,962
Acquisition expenses	25,986	1,706	7,037
Other expenses	18,540	16,553	13,521
Total noninterest expenses	347,149	266,848	233,055
Income before income taxes	159,965	154,597	132,217
Income taxes	9,248	50,785	40,987
Net income	$ 150,717	$ 103,812	$ 91,230
Basic earnings per share (in dollars per share)	$ 3.07	$ 2.34	$ 2.21
Diluted earnings per share (in dollars per share)	3.03	2.32	2.19
Cash dividends declared per share (in dollars per share)	$ 1.32	$ 1.26	$ 1.22