Consolidated Statements of Income - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
INTEREST INCOME:
Interest and fees on loans	$ 393,871,000	$ 304,006,000	$ 278,128,000
Interest on securities:
Taxable	54,131,000	38,365,000	32,858,000
Nontaxable	14,120,000	19,698,000	15,085,000
Interest on federal funds sold	0	42,000	12,000
Interest on interest bearing deposits in other financial institutions	3,698,000	1,547,000	396,000
TOTAL INTEREST INCOME	465,820,000	363,658,000	326,479,000
INTEREST EXPENSE:
Interest on deposits	35,667,000	18,279,000	15,939,000
Interest on short-term borrowings	1,696,000	678,000	1,202,000
Interest on other borrowings (includes $179, $1,290 and $1,914 of interest expense related to derivatives reclassified from accumulated other comprehensive loss for the years ended December 31, 2018, 2017, and 2016, respectively)	14,503,000	14,393,000	14,672,000
TOTAL INTEREST EXPENSE	51,866,000	33,350,000	31,813,000
NET INTEREST INCOME	413,954,000	330,308,000	294,666,000
Provision for loan losses	24,013,000	15,563,000	11,694,000
NET INTEREST INCOME AFTER PROVISION FOR LOAN LOSSES	389,941,000	314,745,000	282,972,000
NONINTEREST INCOME:
Revenue from contract with customers	71,612,000	59,034,000	50,304,000
Loan servicing income	7,292,000	5,636,000	4,501,000
Securities gains, net (includes $1,085, $6,764, and $11,518 of net security gains reclassified from accumulated other comprehensive income for the years ended December 31, 2018, 2017, and 2016, respectively)	1,085,000	6,973,000	11,340,000
Unrealized gain on equity securities, net	212,000	0	0
Net gains on sale of loans held for sale	21,450,000	22,251,000	39,634,000
Valuation allowance on servicing rights	(46,000)	21,000	(33,000)
Income on bank owned life insurance	2,793,000	2,772,000	2,275,000
Other noninterest income	4,762,000	5,335,000	5,580,000
TOTAL NONINTEREST INCOME	109,160,000	102,022,000	113,601,000
NONINTEREST EXPENSES:
Salaries and employee benefits	196,118,000	171,407,000	163,547,000
Occupancy	25,328,000	22,244,000	20,398,000
Furniture and equipment	12,529,000	11,061,000	10,245,000
Professional fees	39,811,000	32,879,000	27,676,000
FDIC insurance assessments	3,699,000	3,595,000	4,185,000
Advertising	9,565,000	7,229,000	6,448,000
Core deposit intangibles and customer relationship intangibles amortization	9,355,000	6,077,000	5,630,000
Other real estate and loan collection expenses	3,038,000	2,461,000	2,443,000
Loss on sales/valuations of assets, net	2,208,000	2,475,000	1,478,000
Restructuring expenses	2,564,000	0	0
Other noninterest expenses	49,673,000	38,247,000	37,618,000
TOTAL NONINTEREST EXPENSES	353,888,000	297,675,000	279,668,000
Income (loss) before income taxes	145,213,000	119,092,000	116,905,000
Income taxes (includes $165, $2,042, and $3,582 of income tax expense reclassified from accumulated other comprehensive income (loss) for the years ended December 31, 2018, 2017, and 2016, respectively)	28,215,000	43,820,000	36,556,000
NET INCOME	116,998,000	75,272,000	80,349,000
Preferred dividends	(39,000)	(58,000)	(292,000)
Interest expense on convertible preferred debt	0	12,000	51,000
NET INCOME AVAILABLE TO COMMON STOCKHOLDERS	$ 116,959,000	$ 75,226,000	$ 80,108,000
EARNINGS PER COMMON SHARE - BASIC (in dollars per share)	$ 3.54	$ 2.67	$ 3.26
EARNINGS PER COMMON SHARE - DILUTED (in dollars per share)	3.52	2.65	3.22
CASH DIVIDENDS DECLARED PER COMMON SHARE (in dollars per share)	$ 0.59	$ 0.51	$ 0.50
Service charges and fees
NONINTEREST INCOME:
Revenue from contract with customers	$ 48,706,000	$ 39,183,000	$ 31,590,000
Trust fees
NONINTEREST INCOME:
Revenue from contract with customers	18,393,000	15,818,000	14,845,000
Brokerage and insurance commissions
NONINTEREST INCOME:
Revenue from contract with customers	$ 4,513,000	$ 4,033,000	$ 3,869,000