Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 52,398	$ 40,591	$ 47,856
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation expense	4,316	3,995	3,283
Amortization of core deposit and other intangibles	1,995	2,132	1,731
Capitalization of mortgage servicing rights	(58,984)	(46,070)	(26,474)
Amortization of mortgage servicing rights		8,321	2,601
Change in fair value of mortgage servicing rights	4,023
Impairment of mortgage servicing rights		4,678	194
Stock-based compensation expense	6,760	4,693
Provision for loan losses	(950)	(1,479)	(3,064)
Provision for mortgage loan repurchases	810	512	1,375
Accretion of yield on purchased loans	(5,419)	(3,538)	(493)
Accretion of discounts and amortization of premiums on securities, net	2,693	2,326	1,474
Bargain purchase gain			(2,794)
Gain from securities, net	(285)	(4,407)	(1,844)
Originations of loans held for sale	(6,331,458)	(4,671,561)	(2,757,463)
Proceeds from sale of loans held for sale	6,408,198	4,534,837	2,739,914
Gain on sale and change in fair value of loans held for sale	(107,189)	(115,485)	(65,947)
Loss (gain) on sale of mortgage servicing rights	249	(3,406)
Net gain or write-downs of other real estate owned	(774)	(1,282)	317
Gain on other assets	664	103	393
Provision for deferred income taxes	6,458	9,257	1,647
Changes in:
Other assets and interest receivable	6,478	(24,730)	(1,301)
Accrued expenses and other liabilities	47,627	15,312	12,820
Net cash provided by (used in) operating activities	37,610	(245,201)	(45,775)
Activity in available-for-sale securities:
Sales	94,743	271,148	194,611
Maturities, prepayments and calls	83,344	104,368	103,233
Purchases	(81,353)	(316,384)	(164,864)
Net increase in loans	(241,379)	(127,949)	(206,670)
Proceeds from sale of mortgage servicing rights	11,686	34,118
Purchases of premises and equipment	(4,545)	(4,784)	(5,918)
Proceeds from the sale of premises and equipment	39	46	17
Proceeds from the sale of other real estate owned	5,438	6,696	3,774
Net cash (paid) received in business combination	(135,141)		23,995
Net cash used in investing activities	(267,168)	(32,741)	(51,822)
Cash flows from financing activities:
Net increase in demand and savings deposits	14,682	167,616	306,360
Net (decrease) increase in time deposits	(1,367)	65,472	(37,671)
Net decrease in securities sold under agreements to repurchase	(7,268)	(83,572)	(8,361)
Increase (decrease) in short-term borrowings	23,767	132,000	(81,378)
Increase (decrease) in long-term debt	29,812	(11,724)	(8,234)
Net proceeds from sale of common stock	153,356	116,054
Dividends paid		(69,300)	(25,350)
Net cash provided by financing activities	212,982	316,546	145,366
Net change in cash and cash equivalents	(16,576)	38,604	47,769
Cash and cash equivalents at beginning of the period	136,327	97,723	49,954
Cash and cash equivalents at end of the period	119,751	136,327	97,723
Supplemental cash flow information:
Interest paid	15,470	9,474	8,985
Taxes paid	22,292	1,307	1,754
Supplemental noncash disclosures:
Transfers from loans to other real estate owned	3,605	2,724	4,085
Transfers from other real estate owned to loans	256	1,548	785
Transfers from loans held for sale to loans	11,706	17,963	$ 5,045
Rebooked GNMA loans under optional repurchase program	43,035
Stock consideration paid in business combination	52,284
Conversion of cash-settled to stock settled compensation		$ 5,388
Trade date payable - securities	348
Fair value election of mortgage servicing rights	$ 1,011