CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest income:
Interest and fees on loans	$ 211,467	$ 187,743	$ 185,527
Interest and dividends on taxable investments	56,201	52,871	50,247
Interest and dividends on nontaxable investments	17,519	19,008	20,446
Total interest income	285,187	259,622	256,220
Interest expense:
Interest on deposits	7,325	6,971	8,191
Interest on borrowings	1,017	1,694	1,124
Interest on subordinated debt held by unconsolidated subsidiary trusts	2,949	2,537	2,477
Total interest expense	11,291	11,202	11,792
Net interest income	273,896	248,420	244,428
Provision for loan losses	8,076	6,447	7,178
Net interest income after provision for loan losses	265,820	241,973	237,250
Noninterest income:
Deposit service fees	58,595	52,747	52,756
Other banking revenues	7,477	4,960	5,814
Employee benefit services	46,628	45,388	42,580
Insurance services	23,149	3,352	1,450
Wealth management services	19,776	16,856	16,420
Loss on sales of investment securities, net	0	(4)	0
Total noninterest income	155,625	123,299	119,020
Noninterest expenses:
Salaries and employee benefits	151,647	126,356	123,077
Occupancy and equipment	30,078	27,593	27,948
Data processing and communications	34,501	30,430	29,294
Amortization of intangible assets	5,479	3,663	4,287
Legal and professional fees	8,455	6,813	7,247
Office supplies and postage	7,274	6,476	6,270
Business development and marketing	7,484	7,204	7,125
FDIC insurance premiums	3,671	3,962	3,899
Acquisition expenses	1,706	7,037	123
Other expenses	16,553	13,521	17,310
Total noninterest expenses	266,848	233,055	226,580
Income before income taxes	154,597	132,217	129,690
Income taxes	50,785	40,987	38,337
Net income	$ 103,812	$ 91,230	$ 91,353
Basic earnings per share (in dollars per share)	$ 2.34	$ 2.21	$ 2.24
Diluted earnings per share (in dollars per share)	2.32	2.19	2.22
Cash dividends declared per share (in dollars per share)	$ 1.26	$ 1.22	$ 1.16