CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - UNAUDITED - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Operating activities:
Net income	$ 29,383	$ 29,234	$ 87,976	$ 75,298
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization			10,006	9,265
Provision for loan losses	1,524	1,890	3,029	5,620	$ 9,023
Stock based compensation expense			2,259	1,941
Tax benefits associated with share based compensation			75	250
Deferred Income Tax Expense (Benefit)			455	6,959
Origination of loans held for sale			(638,820)	(321,224)
Proceeds from sales of loans held for sale			590,997	331,212
Gains on sales of loans held for sale			(8,225)	(5,809)
Losses on sales of other real estate owned			173	104
Investment securities gains	(15)	(82)	(20)	(145)
Increase (Decrease) in Operating Capital [Abstract]
Net (increase) decrease in accrued interest receivable			1,171	(2,072)
Net decrease (increase) in other assets			(3,997)	1,653
Net decrease in accrued expenses and other liabilities			(4,510)	(3,160)
Other - net			2,341	3,988
Net cash provided by operating activities			42,910	103,880
Investing activities:
(Purchases) of other equity securities				(3,659)
Proceeds from other equity securities			21,451
Purchases of investments available-for-sale			(83,835)	(55,251)
Proceeds from sales of investment available-for-sale			0	34,691
Proceeds from maturities, calls and principal payments of investments available-for-sale			141,880	83,789
Net increase in loans			(25,327)	(454,760)
Proceeds from the sales of other real estate owned			324	759
Proceeds from sales of loans previously held for investment			0	59,945
Acquisition of business activity, net of cash paid			0	32,552
Expenditures for premises and equipment			(4,269)	(8,545)
Net cash provided/ (used) by investing activities			50,224	(310,479)
Financing activities:
Net increase in deposits			579,019	323,890
Net increase/(decrease) in retail repurchase agreements and federal funds purchased			(201,421)	16,424
Proceeds from advances from FHLB			2,123,000	4,930,000
Repayment of advances from FHLB			(2,454,134)	(5,068,745)
Proceeds from issuance of common stock			1,068	1,140
Stock tendered for payment of withholding taxes			(702)	(760)
Dividends paid			(31,509)	(29,273)
Net cash provided/ (used) by financing activities			15,321	172,676
Net increase (decrease) in cash and cash equivalents			108,455	(33,923)
Cash and cash equivalents at beginning of period			101,481	112,500	112,500
Cash and cash equivalents at end of period	$ 209,936	$ 78,577	209,936	78,577	$ 101,481
Supplemental Disclosures:
Interest payments			65,481	42,279
Income tax payments			23,417	19,092
Transfer from loans to residential mortgage loans held for sale			0	60,043
Transfers from loans to other real estate owned			$ 414	$ 289