Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ 72,253	$ 70,871
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	7,528	8,913
Net loss on disposal of premises and equipment	0	492
Depreciation and amortization	17,920	14,482
Net premium amortization on investment securities	8,464	9,423
Net gain on investment securities transactions	(778)	(312)
Realized and unrealized net gains on mortgage banking activities	(15,353)	(15,126)
Net gain on sale of OREO	(375)	(693)
Write-downs of OREO and other assets pending disposal	294	621
Net (gain) on sale of Health Savings Accounts	(3,068)	0
Mortgage servicing rights recovery	(84)	(21)
Deferred income tax expense (benefit)	19,771	(344)
Net increase in cash surrender value of company-owned life insurance	(3,775)	(3,431)
Stock-based compensation expense	3,418	3,350
Tax benefits from stock-based compensation expense	0	1,352
Excess tax benefits from stock-based compensation expense	0	(1,126)
Originations of mortgage loans held for sale	(980,551)	(799,445)
Proceeds from sales of mortgage loans held for sale	992,409	795,527
Changes in operating assets and liabilities, net of effects of acquisition:
(Increase) decrease in interest receivable	(3,164)	(2,203)
Decrease (increase) in other assets	(4,784)	(2,644)
Increase in accrued interest payable	227	646
Increase (decrease) in accounts payable and accrued expenses	(15,658)	(1,278)
Net cash provided by operating activities	94,694	79,054
Cash flows from investing activities:
Purchase of investment securities, Held-to-maturity	(12,793)	(18,170)
Purchase of investment securities, Available-for-sale	(386,527)	(626,574)
Proceeds from maturities and paydowns of held-to-maturity investment securities	76,027	86,306
Proceeds from maturities and paydowns of available-for-sale investment securities	319,958	652,064
Extensions of credit to customers, net of repayments	(20,885)	(203,216)
Recoveries of loans charged-off	6,452	6,363
Proceeds from sale of OREO	4,150	3,352
Acquisition of intangible assets	(28,013)	0
Proceeds from the sale of Health Savings Accounts	6,138	0
Proceeds from sale of loan production office	0	932
Acquisition of bank and bank holding company, net of cash and cash equivalents received	91,775	18,554
Capital expenditures, net of sales	(12,237)	(5,113)
Net cash provided by (used in) investing activities	44,045	(85,502)
Cash flows from financing activities:
Net increase (decrease) in deposits	(111,618)	30,057
Net increase (decrease) in securities sold under repurchase agreements	97,732	(51,917)
Net increase in other borrowed funds	10,000	6
Repayments of long-term debt	(69)	(49)
Advances on long-term debt	0	113
Proceeds from issuance of common stock	1,988	3,657
Excess tax benefits from stock-based compensation expense	0	1,126
Purchase and retirement of common stock	(938)	(26,119)
Dividends paid to common stockholders	(35,024)	(29,516)
Net cash used in financing activities	(37,929)	(72,642)
Net increases (decrease) in cash and cash equivalents	100,811	(79,090)
Cash and cash equivalents at beginning of period	782,023	780,457
Cash and cash equivalents at end of period	882,834	701,367
Supplemental disclosures of cash flow information:
Cash paid during the period for income taxes	24,279	40,416
Cash paid during the period for interest expense	19,857	12,448
Noncash or Part Noncash Acquisition, Value of Assets Acquired [Abstract]
Transfer of loans to loans held for sale	6,270	50
Transfer from long-term debt to other borrowed funds	20,000	0
Transfer of loans to other real estate owned	3,182	5,335
Capitalization of internally originated mortgage servicing rights	4,147	3,890
Investment securities available for sale	424,302	0
Investment securities held to maturity	57,307	0
Loans held for sale	10,259	0
Loans	2,080,374	0
Premises and equipment	46,732	0
Goodwill	232,208	0
Core deposit intangible	47,968	0
Mortgage servicing rights	3,491	0
Interest receivable	7,605	0
Company-owned life insurance	57,038	0
Deferred tax assets	25,992	0
Other real estate owned	1,192	0
Other assets	31,572	0
Total noncash assets acquired	3,026,040	0
Liabilities assumed:
Deposits	2,668,976	0
Accounts payable and accrued expenses	62,870	0
Total liabilities assumed	$ 2,731,846	$ 0