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	$ 284,020	$ 149,523	$ 108,032
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	30,750	23,300	14,875
Gains on sales of loans	(12,173)	(31,734)	(15,686)
Proceeds from sales of loans	741,902	838,549	723,521
Loans originated for sale	(760,591)	(772,968)	(534,422)
Net losses (gains) on sale of investment securities	(224)	7,388	(129)
Net losses (gains) from sales/writedowns of other real estate and repossessed assets	203	(1,017)	(5,212)
Depreciation of premises and equipment	17,026	17,722	13,270
Amortization of intangible assets	5,716	6,090	10,046
Additions to loan servicing rights	(8,226)	(8,745)	(4,333)
Valuation change in loan servicing rights	1,054	8,880	(4,585)
Net amortization of premiums and discounts on investment securities	19,446	19,262	9,713
Share-based compensation expense	8,578	17,346	13,452
Deferred income tax expense	41,916	93,184	24,091
Change in deferred tax valuation allowance	317	(1,089)	(706)
Net increase in interest receivable and other assets	(74,723)	(150,585)	(24,977)
Net increase (decrease) in interest payable and other liabilities	29,410	59,760	(46,449)
Net cash provided by operating activities	324,401	274,866	280,501
Investment securities — carried at fair value:
Proceeds from maturities, calls and principal reductions	291,008	318,952	248,772
Proceeds from sales and redemptions	4,215	409,220	41,446
Purchases	(1,405,798)	(1,480,524)	(187,702)
Investment securities — held-to-maturity:
Proceeds from maturities, calls and principal reductions	104,535	93,600	90,933
Purchases	(52,752)	(141,489)	(206,023)
Net increase in loans	(1,140,686)	(1,189,865)	(860,135)
Proceeds from sales of other real estate and repossessed assets	13,396	19,879	22,147
Purchases of premises and equipment, net of disposals	(13,572)	(12,852)	(18,098)
Proceeds from returns of investment in equity method investments	326	143	77
Cash acquired, net of cash paid, in business combinations	0	0	325,714
Net cash used in investing activities	(2,199,328)	(1,982,936)	(542,869)
Cash flows from financing activities
Net increase in interest and noninterest-bearing demand deposits and savings accounts	1,111,747	243,110	672,584
Net increase (decrease) in time deposits	838,732	526,571	(550,847)
Net increase in collateralized customer deposits and other short-term borrowings	2,451	1,247,189	401,144
Proceeds from issuance of long-term borrowings	200,000	0	375,000
Repayment of long-term borrowings	(147,000)	(224,850)	(351,018)
Cash dividends paid	(88,954)	(78,498)	(49,389)
Proceeds from directors' stock plans and exercise of stock options, net of shares withheld	3,115	3,991	1,572
Cash paid for payroll taxes upon conversion of share-based awards	(5,316)	(27,854)	(1,065)
Net cash provided by financing activities	1,914,775	1,689,659	497,981
Net increase (decrease) in cash and cash equivalents	39,848	(18,411)	235,613
Cash and cash equivalents at beginning of year	455,991	474,402	238,789
Cash and cash equivalents at end of year	495,839	455,991	474,402
Supplemental disclosures of cash flow information:
Interest paid	136,706	73,643	25,460
Income tax payments, net	4,063	2,252	22,200
Non-cash activities:
Loans transferred to other real estate and repossessed assets	11,486	11,546	12,970
Net transfer of loans held-for-sale to loans held- for-investment	(2,035)	(4,150)	(289)
Closed branch offices transferred to other assets	0	13,246	4,846
Business combinations:
Fair value of tangible assets acquired (noncash)	0	420	6,371,781
Goodwill, loan servicing rights and other identifiable intangible assets acquired	0	1,034	908,217
Liabilities assumed	0	1,454	6,100,901
Common stock and stock options issued	$ 0	$ 0	$ 1,504,811