CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Operating activities:
Net income	$ 21,665	$ 15,112
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	2,990	1,980
Provision for loan losses	1,997	194	$ 2,977
Stock based compensation expense	582	496
Tax benefits associated with share based compensation	34	239
Deferred income tax expense	(1,673)	(214)
Origination of loans held for sale	(47,975)	(34,895)
Proceeds from sales of loans held for sale	58,121	41,850
(Gains)/ losses on sales of loans held for sale	(2,872)	924
(Gains) losses on sales of other real estate owned	90	(17)
Investment securities gains	(63)	(2)
Increase (Decrease) in Operating Capital [Abstract]
Net (increase) decrease in accrued interest receivable	(397)	57
Net decrease in other assets	11,407	(195)
Net increase (decrease) in accrued expenses and other liabilities	(403)	6,076
Other - net	754	2,654
Net cash provided by operating activities	44,257	34,259
Investing activities:
Proceeds of other equity securities		4,483
Purchases of investments held-to-maturity	(700)
Purchases of investments available-for-sale	(497)	(105,028)
Proceeds from sales of investment available-for-sale	994	0
Proceeds from maturities, calls and principal payments of investments held-to-maturity	0	0
Proceeds from maturities, calls and principal payments of investments available-for-sale	23,975	25,296
Net increase in loans	(123,945)	(77,674)
Proceeds from the sales of other real estate owned	292	759
Proceeds from sales of loans held for investment	59,945	0
Acquisition of business activity, net of cash acquired	32,552	0
Expenditures for premises and equipment	(2,842)	(1,131)
Net cash (used) in investing activities	(10,226)	(153,295)
Financing activities:
Net increase in deposits	52,702	221,654
Net increase/(decrease) in retail repurchase agreements and federal funds purchased	23,078	16,125
Proceeds from advances from FHLB	1,990,000	1,130,000
Repayment of advances from FHLB	(1,984,081)	(1,245,000)
Retirement of subordinated debt	0	(30,000)
Proceeds from issuance of common stock	456	276
Stock tendered for payment of withholding taxes	0	0
Repurchase of common stock	0	0
Dividends paid	(9,267)	(6,275)
Net cash provided by financing activities	72,888	86,780
Net increase (decrease) in cash and cash equivalents	106,919	(32,256)
Cash and cash equivalents at beginning of period	112,500	134,125	134,125
Cash and cash equivalents at end of period	219,419	101,869	$ 112,500
Supplemental Disclosures:
Interest payments	11,680	5,936
Income tax payments	15	7
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	12,374
Transfers from loans to other real estate owned	$ 289	$ 113