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	$ 149,523	$ 108,032	$ 86,830
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	23,300	14,875	6,500
Gains on sales of loans	(31,734)	(15,686)	(6,354)
Proceeds from sales of loans	838,549	723,521	228,995
Loans originated for sale	(772,968)	(534,422)	(220,765)
Net losses (gains) on sale of investment securities	7,388	(129)	(630)
Net gains from sales/writedowns of other real estate and repossessed assets	(1,017)	(5,212)	(2,681)
Depreciation of premises and equipment	17,722	13,270	11,028
Amortization of intangible assets	6,090	10,046	8,444
Additions to loan servicing rights	(8,745)	(4,333)	(1,476)
Valuation change in loan servicing rights	8,880	(4,585)	(200)
Net amortization of premiums and discounts on investment securities	19,262	9,713	6,007
Share-based compensation expense	17,346	13,452	3,478
Deferred income tax expense	93,184	24,091	5,700
Net increase in interest receivable and other assets	(151,531)	(25,606)	(19,027)
Net increase (decrease) in interest payable and other liabilities	59,760	(46,449)	(2,800)
Net cash from operating activities	275,009	280,578	103,049
Investment securities — available-for-sale:
Proceeds from maturities, calls and principal reductions	318,952	248,772	212,051
Proceeds from sales and redemptions	409,220	41,446	40,301
Purchases	(1,480,524)	(187,702)	0
Investment securities — held-to-maturity:
Proceeds from maturities, calls and principal reductions	93,600	90,933	87,189
Purchases	(141,489)	(206,023)	(279,226)
Net increase in loans	(1,189,865)	(860,135)	(493,776)
Proceeds from sales of other real estate and repossessed assets	19,879	22,147	16,653
Purchases of premises and equipment, net of disposals	(12,852)	(18,098)	(8,527)
Cash acquired, net of cash paid, in business combinations	0	325,714	16,551
Net cash used in investing activities	(1,983,079)	(542,946)	(408,784)
Cash flows from financing activities
Net increase in interest- and noninterest-bearing demand deposits and savings accounts	243,110	672,584	479,386
Net increase (decrease) in time deposits	526,571	(550,847)	(170,598)
Net increase (decrease) in securities sold under agreements to repurchase with customers and other short-term borrowings	1,247,189	401,144	(31,268)
Proceeds from issuance of long-term borrowings	0	375,000	125,000
Repayment of long-term borrowings	(224,850)	(351,018)	(6,000)
Cash dividends paid	(78,498)	(49,389)	(36,918)
Proceeds from directors' stock plans and exercise of stock options, net of shares withheld	3,991	1,572	2,473
Cash paid for payroll taxes upon conversion of share-based awards	(27,854)	(1,065)	(571)
Net cash from financing activities	1,689,659	497,981	361,504
Net increase (decrease) in cash and cash equivalents	(18,411)	235,613	55,769
Cash and cash equivalents at beginning of year	474,402	238,789	183,020
Cash and cash equivalents at end of year	455,991	474,402	238,789
Supplemental disclosures of cash flow information:
Interest paid	73,643	25,460	16,958
Net income tax payments	2,252	22,200	41,450
Non-cash activities:
Loans transferred to other real estate and repossessed assets	11,546	12,970	9,329
Net transfer of loans held-for-sale to loans held- for-investment	(4,150)	(289)	0
Closed branch offices transferred to other assets	13,246	4,846	2,692
Business combinations:
Fair value of tangible assets acquired (noncash)	420	6,371,781	1,282,420
Goodwill, loan servicing rights and other identifiable intangible assets acquired	1,034	908,217	118,744
Liabilities assumed	1,454	6,100,901	1,258,051
Common stock and stock options issued	$ 0	$ 1,504,811	$ 159,904