CONSOLIDATED STATEMENTS OF CASH FLOWS	12 Months Ended
	Dec. 31, 2018 USD ($)		Dec. 31, 2017 USD ($)		Dec. 31, 2016 USD ($)
OPERATING ACTIVITIES
Net income	$ 74,138,000		$ 54,312,000		$ 49,349,000
Adjustments to reconcile net income to net cash provided by operations:
Depreciation and net amortization	14,045,000		10,208,000		9,084,000
Securities premium amortization (discount accretion), net	13,675,000		17,639,000		19,126,000
Loan (discount accretion) premium amortization, net	(2,333,000)		(1,142,000)		(2,520,000)
Provision for loan losses	8,437,000	[1]	4,675,000	[1]	9,780,000	[1]
Stock compensation expense	2,317,000		1,815,000		1,541,000
Deferred tax expense	6,154,000		3,514,000		1,768,000
Net tax benefit related to stock awards	0		0		(332,000)
Net loss (gain) on sale of securities available for sale	1,839,000		(625,000)		(2,836,000)
Net loss on premises and equipment	768,000		152,000		376,000
Gross proceeds from sales of loans held for sale	24,092,000		58,747,000		82,062,000
Gross originations of loans held for sale	(22,692,000)		(53,107,000)		(85,892,000)
Net loss on other real estate owned	433,000		7,000		219,000
Net gain on sale of customer receivables	(124,000)		0		(194,000)
Net change in:
Interest receivable	1,204,000		(63,000)		(2,483,000)
Other assets	(2,166,000)		(3,909,000)		1,823,000
Interest payable	1,257,000		570,000		2,334,000
Other liabilities	1,358,000		(1,063,000)		3,520,000
Net cash provided by operating activities	122,402,000		91,730,000		86,725,000
Securities available for sale:
Purchases	(306,867,000)		(619,398,000)		(1,001,742,000)
Sales	428,518,000		685,152,000		573,051,000
Maturities, calls and principal repayments	137,883,000		113,183,000		207,500,000
Securities held to maturity:
Purchases	0		(6,260,000)		(44,656,000)
Maturities, calls and principal repayments	3,064,000		28,974,000		31,251,000
Proceeds from redemption of FHLB stock and other investments	24,360,000		6,945,000		3,644,000
Purchases of FHLB stock and other investments	(1,518,000)		(1,233,000)		(13,667,000)
Net loan originations	(24,491,000)		(117,750,000)		(139,607,000)
Proceeds from sales of customer receivables	4,300,000		0		3,325,000
Net cash and cash equivalents acquired in acquisition	0		115,598,000		0
Net cash paid in acquisition	0		(23,941,000)		0
Purchases of premises and equipment	(13,444,000)		(9,633,000)		(6,549,000)
Proceeds from bank owned life insurance	5,956,000		0		0
Proceeds from sales of premises and equipment	1,943,000		12,000		128,000
Proceeds from sales of other real estate owned	1,717,000		659,000		2,024,000
Proceeds from sales of repossessed assets	483,000		429,000		894,000
Net cash provided by (used in) investing activities	261,904,000		172,737,000		(384,404,000)
FINANCING ACTIVITIES:
Net change in deposits	(106,014,000)		82,960,000		78,426,000
Net increase in federal funds purchased and repurchase agreements	27,312,000		2,401,000		4,668,000
Proceeds from FHLB borrowings	4,201,500,000		2,786,476,000		8,158,985,000
Repayment of FHLB borrowings	(4,499,788,000)		(3,078,743,000)		(7,996,913,000)
Net proceeds from issuance of subordinated long-term debt	0		0		98,060,000
Tax benefit related to stock awards	0		0		332,000
Proceeds from stock option exercises	2,653,000		2,692,000		1,663,000
Cash paid to tax authority related to tax withholding on share-based awards	(248,000)		(222,000)		(104,000)
Purchase of common stock	(47,193,000)		0		(10,199,000)
Proceeds from the issuance of common stock for dividend reinvestment plan	1,478,000		1,483,000		1,411,000
Proceeds from the issuance of common stock	0		0		75,992,000
Cash dividends paid	(41,979,000)		(32,199,000)		(25,963,000)
Payments for other financing activities	0		(277,000)		0
Net cash (used in) provided by financing activities	(462,279,000)		(235,429,000)		386,358,000
Net (decrease) increase in cash and cash equivalents	(77,973,000)		29,038,000		88,679,000
Cash and cash equivalents at beginning of period	198,692,000		169,654,000		80,975,000
Cash and cash equivalents at end of period	120,719,000		198,692,000		169,654,000
SUPPLEMENTAL DISCLOSURES FOR CASH FLOW INFORMATION:
Interest paid	55,844,000		42,934,000		27,014,000
Income taxes paid	2,000,000		11,300,000		5,700,000
SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Loans transferred to other repossessed assets and real estate through foreclosure	2,128,000		574,000		5,777,000
Loans transferred from portfolio to held for sale	3,984,000		0		0
Transfer of held to maturity securities to available for sale securities	743,421,000		0		0
Transfer of available for sale securities to held to maturity securities	0		0		157,083,000
Adjustment to pension liability	188,000		3,605,000		1,441,000
Stock dividend (2.5% for 2017, 5% for 2016)	0		24,960,000		34,765,000
Unsettled trades to purchase securities	(6,378,000)		0		(160,000)
Unsettled issuances of brokered certificates of deposit	15,236,000		0		0
Common stock issued in acquisition	$ 0		$ 200,364,000		$ 0

[1] Of the $8.4 million in provision for loan losses for the year ended December 31, 2018, $302,000 related to provision expense on PCI loans. Of the $4.7 million and $9.8 million recorded in provision for loan losses for the year ended December 31, 2017 and 2016, respectively, none related to provision expense on PCI loans