CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Interest income:
Interest and fees on loans	$ 187,743	$ 185,527	$ 188,197
Interest and dividends on taxable investments	52,871	50,247	54,995
Interest and dividends on nontaxable investments	19,008	20,446	20,967
Total interest income	259,622	256,220	264,159
Interest expense:
Interest on deposits	6,971	8,191	10,732
Interest on borrowings	1,694	1,124	12,813
Interest on subordinated debt held by unconsolidated subsidiary trusts	2,537	2,477	2,520
Total interest expense	11,202	11,792	26,065
Net interest income	248,420	244,428	238,094
Provision for loan losses	6,447	7,178	7,992
Net interest income after provision for loan losses	241,973	237,250	230,102
Noninterest income:
Deposit service fees	52,747	52,756	49,357
Other banking revenues	4,960	5,814	5,245
Employee benefit services	45,388	42,580	38,596
Wealth management and insurance services	20,208	17,870	15,550
(Loss)/Gain on sales of investment securities, net	(4)	0	80,768
Loss on debt extinguishments	0	0	(87,336)
Total noninterest income	123,299	119,020	102,180
Noninterest expenses:
Salaries and employee benefits	126,356	123,077	121,629
Occupancy and equipment	27,593	27,948	27,045
Data processing and communications	30,430	29,294	27,186
Amortization of intangible assets	3,663	4,287	4,469
Legal and professional fees	6,813	7,247	7,008
Office supplies and postage	6,476	6,270	6,122
Business development and marketing	7,204	7,125	6,815
FDIC insurance premiums	3,962	3,899	3,829
Acquisition expenses	7,037	123	2,181
Other expenses	13,521	17,310	14,971
Total noninterest expenses	233,055	226,580	221,255
Income before income taxes	132,217	129,690	111,027
Income taxes	40,987	38,337	32,198
Net income	$ 91,230	$ 91,353	$ 78,829
Basic earnings per share (in dollars per share)	$ 2.21	$ 2.24	$ 1.96
Diluted earnings per share (in dollars per share)	2.19	2.22	1.94
Cash dividends declared per share (in dollars per share)	$ 1.22	$ 1.16	$ 1.10