Consolidated statements of cash flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 80,236	$ 52,398	$ 40,591
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation expense	4,334	4,316	3,995
Amortization of core deposit and other intangibles	3,185	1,995	2,132
Capitalization of mortgage servicing rights	(54,913)	(58,984)	(46,070)
Amortization of mortgage servicing rights	0	0	8,321
Net change in fair value of mortgage servicing rights	2,763	4,023	0
Impairment of mortgage servicing rights	0	0	4,678
Stock-based compensation expense	7,207	6,760	4,693
Provision for loan losses	5,398	(950)	(1,479)
Provision for mortgage loan repurchases	174	810	512
Accretion of yield on purchased loans	(7,608)	(5,419)	(3,538)
Accretion of discounts and amortization of premiums on securities, net	2,768	2,693	2,326
Loss (gain) from securities, net	116	(285)	(4,407)
Originations of loans held for sale	(5,958,066)	(6,331,458)	(4,671,561)
Repurchases of loans held for sale	(12,232)	0	0
Proceeds from sale of loans held for sale	6,260,532	6,408,198	4,534,837
Gain on sale and change in fair value of loans held for sale	(88,743)	(107,189)	(115,485)
Loss (gain) on sale of mortgage servicing rights	0	249	(3,406)
Net (gain) or write-downs of other real estate owned	99	(774)	(1,282)
(Gain) loss on other assets	(328)	664	103
Provision for deferred income taxes	6,359	6,458	9,257
Changes in:
Other assets and interest receivable	(22,966)	6,478	(24,730)
Accrued expenses and other liabilities	(16,107)	47,627	15,312
Net cash provided by (used in) operating activities	212,208	37,610	(245,201)
Activity in available-for-sale securities:
Sales	2,742	94,743	271,148
Maturities, prepayments and calls	73,066	83,344	104,368
Purchases	(203,844)	(81,353)	(316,384)
Net increase in loans	(491,774)	(241,379)	(127,949)
Purchases of FHLB stock	(2,020)	0	0
Proceeds from sale of mortgage servicing rights	39,428	11,686	34,118
Purchases of premises and equipment	(10,144)	(4,545)	(4,784)
Proceeds from the sale of premises and equipment	357	39	46
Proceeds from the sale of other real estate owned	4,819	5,438	6,696
Proceeds from the sale of other assets	869	0	0
Net cash paid in business combination	0	(135,141)	0
Net cash used in investing activities	(586,501)	(267,168)	(32,741)
Cash flows from financing activities:
Net increase in demand deposits	75,906	14,682	167,616
Net increase (decrease) in time deposits	431,416	(1,367)	65,472
Net (decrease) increase in borrowings	(119,819)	46,311	36,704
Share based compensation withholding obligation	(2,664)	0	0
Net proceeds from sale of common stock	1,196	153,356	116,054
Dividends paid	(6,137)	0	(69,300)
Net cash provided by financing activities	379,898	212,982	316,546
Net change in cash and cash equivalents	5,605	(16,576)	38,604
Cash and cash equivalents at beginning of the period	119,751	136,327	97,723
Cash and cash equivalents at end of the period	125,356	119,751	136,327
Supplemental cash flow information:
Interest paid	31,992	15,470	9,474
Taxes paid	24,387	22,292	1,307
Supplemental noncash disclosures:
Transfers from loans to other real estate owned	2,138	3,605	2,724
Transfers from other real estate owned to loans	1,019	256	1,548
Transfers from loans held for sale to loans	14,732	11,706	17,963
Transfers from loans to loans held for sale	11,888	0	0
Stock consideration paid in business combination	0	52,284	0
Conversion of cash-settled to stock settled compensation	0	0	5,388
Trade date payable - securities	2,120	348	0
Dividends declared not paid on restricted stock units	226	0	0
Adoption of ASU 2016-01 (See Note 1)	(109)	0	0
Fair value election of mortgage servicing rights	0	1,011	0
GNMA
Supplemental noncash disclosures:
Transfers from loans to loans held for sale	0	43,035	0
Derecognition of rebooked GNMA delinquent loans (See Note 1)	$ 43,035	$ 0	$ 0