Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities
Net income	$ 167,596,000	$ 146,920,000	$ 92,188,000
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	7,050,000	6,810,000	7,550,000
Depreciation, amortization and accretion	8,185,000	3,496,000	4,832,000
Deferred income tax expense	20,041,000	16,444,000	23,461,000
Revaluation of net deferred tax assets due to changes in tax law	0	0	14,486,000
Funding of mortgage loans held for sale	(2,381,178,000)	(1,763,246,000)	(1,683,454,000)
Proceeds from sales of mortgage loans held for sale	2,328,607,000	1,698,141,000	1,775,450,000
Gains on sales of mortgage loans held for sale	(45,854,000)	(40,318,000)	(19,675,000)
Valuation adjustment to mortgage servicing rights	1,836,000	0	0
(Gains) losses on sales of securities	(348,000)	16,000	(148,000)
Penalty on prepayment of debt	54,000	0	205,000
(Gains) losses on sales of premises and equipment	(881,000)	(198,000)	565,000
Stock-based compensation	10,196,000	7,251,000	5,293,000
Net change in other loans held for sale	59,885,000	60,599,000	0
Decrease (increase) in other assets	683,000	(11,849,000)	(1,139,000)
Decrease in other liabilities	(12,249,000)	(41,954,000)	(12,572,000)
Net cash provided by operating activities	163,623,000	82,112,000	207,042,000
Investing activities
Purchases of securities available for sale	(492,018,000)	(686,887,000)	(210,190,000)
Proceeds from sales of securities available for sale	212,485,000	2,387,000	495,340,000
Proceeds from call/maturities of securities available for sale	262,287,000	160,703,000	169,445,000
Proceeds from call/maturities of securities held to maturity	0	0	15,882,000
Net increase in loans	(465,182,000)	(115,208,000)	(440,205,000)
Purchases of premises and equipment	(34,966,000)	(22,360,000)	(13,047,000)
Proceeds from sales of premises and equipment	3,728,000	921,000	2,101,000
Net change in FHLB stock	(11,315,000)	(4,706,000)	(5,481,000)
Proceeds from sales of other assets	18,404,000	8,361,000	14,131,000
Net cash paid in acquisition	(250,000)
Net cash received in acquisition		153,502,000	41,685,000
Other, net	917,000	0	0
Net cash (used in) provided by investing activities	(505,910,000)	(503,287,000)	69,661,000
Financing activities
Net increase in noninterest-bearing deposits	233,064,000	49,087,000	11,588,000
Net (decrease) increase in interest-bearing deposits	(147,139,000)	447,317,000	(88,717,000)
Net increase (decrease) in short-term borrowings	101,385,000	263,753,000	(19,862,000)
Proceeds from long-term debt	150,000,000	0	0
Repayment of long-term debt	(35,359,000)	(849,000)	(170,240,000)
Cash paid for dividends	(50,901,000)	(43,614,000)	(34,416,000)
Repurchase of shares in connection with stock repurchase program	(62,944,000)	(7,062,000)	0
Cash received on exercise of stock options	0	201,000	173,000
Net cash provided by (used in) financing activities	188,106,000	708,833,000	(301,474,000)
Net (decrease) increase in cash and cash equivalents	(154,181,000)	287,658,000	(24,771,000)
Cash and cash equivalents at beginning of year	569,111,000	281,453,000	306,224,000
Cash and cash equivalents at end of year	414,930,000	569,111,000	281,453,000
Supplemental disclosures
Cash paid for interest	98,396,000	66,706,000	36,888,000
Cash paid for income taxes	26,727,000	24,520,000	32,556,000
Noncash transactions:
Transfers of loans to other real estate	4,764,000	3,826,000	6,699,000
Financed sales of other real estate owned	611,000	531,000	773,000
Common stock issued in acquisition of businesses	0	434,519,000	213,590,000
Recognition of operating right-of-use assets	91,181,000
Recognition of operating lease liabilities	94,700,000
Loans Receivable
Noncash transactions:
Transfers of mortgage loans held for sale to loans held for investment	134,335,000	0	0
Mortgage Receivable
Noncash transactions:
Transfers of mortgage loans held for sale to loans held for investment	$ 189,000	$ 1,732,000	$ 563,000