CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Operating activities:
Net income	$ 29,234	$ 15,089	$ 75,298	$ 44,942
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization			9,265	5,939
Provision for loan losses	1,890	934	5,620	2,450	$ 2,977
Stock based compensation expense			1,941	1,611
Tax benefits associated with share based compensation			250	700
Deferred Income Tax Expense (Benefit)			6,959	163
Origination of loans held for sale			(321,224)	(105,970)
Proceeds from sales of loans held for sale			331,212	114,474
(Gains)/ losses on sales of loans held for sale			(5,809)	(2,653)
(Gains) losses on sales of other real estate owned			104	(82)
Investment securities gains	(82)	0	(145)	(1,275)
Increase (Decrease) in Operating Capital [Abstract]
Net (increase) decrease in accrued interest receivable			(2,072)	(1,456)
Net decrease (increase) in other assets			1,653	(5,314)
Net increase (decrease) in accrued expenses and other liabilities			(3,160)	19
Other - net			3,988	3,521
Net cash provided by operating activities			103,880	57,069
Investing activities:
(Purchases) of other equity securities			(3,659)
Proceeds from other equity securities				6,241
Purchases of investments available-for-sale			(55,251)	(125,028)
Proceeds from sales of investment available-for-sale			34,691	2,251
Proceeds from maturities, calls and principal payments of investments available-for-sale			83,789	103,775
Net increase in loans			(454,760)	(306,755)
Proceeds from the sales of other real estate owned			759	1,228
Proceeds from sales of loans previously held for investment			59,945	40,031
Acquisition of business activity, net of cash paid			32,552	0
Expenditures for premises and equipment			(8,545)	(4,589)
Net cash (used) in investing activities			(310,479)	(282,846)
Financing activities:
Net increase in deposits			323,890	378,248
Net increase/(decrease) in retail repurchase agreements and federal funds purchased			16,424	21,450
Proceeds from advances from FHLB			4,930,000	3,080,000
Repayment of advances from FHLB			(5,068,745)	(3,237,083)
Retirement of subordinated debt			0	(30,000)
Proceeds from issuance of common stock			1,140	1,015
Stock tendered for payment of withholding taxes			(760)	(953)
Repurchase of common stock			0	0
Dividends paid			(29,273)	(18,844)
Net cash provided by financing activities			172,676	193,833
Net increase (decrease) in cash and cash equivalents			(33,923)	(31,944)
Cash and cash equivalents at beginning of period			112,500	134,125	134,125
Cash and cash equivalents at end of period	$ 78,577	$ 102,181	78,577	102,181	$ 112,500
Supplemental Disclosures:
Interest payments			42,279	19,244
Income tax payments			19,092	22,927
Transfer of Investments Held-to-maturity to Available For Sale Securities			0	0
Transfer from loans to residential mortgage loans held for sale			60,043	39,744
Transfers from loans to other real estate owned			$ 289	$ 700