Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities:
Net income	$ 23,126	$ 20,124
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	1,730	4,000
Net (gain) loss on disposal of property and equipment	76	142
Depreciation and amortization	4,611	4,679
Net premium amortization on investment securities	2,791	3,238
Net gains on investment securities transactions	(2)	21
Net gains on sales of mortgage loans held for sale	(4,907)	(4,588)
Net gain on sale of OREO	184	(102)
Write-downs of OREO and other assets pending disposal	47	17
Net reversal of impairment of mortgage servicing rights	(70)	15
Deferred income tax expense	2,020	(517)
Net increase in cash surrender value of company-owned life insurance policies	(1,146)	(1,143)
Stock-based compensation expense	877	955
Tax benefits from stock-based compensation expense	0	420
Excess tax benefits from stock-based compensation	0	(307)
Originations of loans held for sale	(193,083)	(195,444)
Proceeds from sales of loans held for sale	235,020	199,316
Changes in operating assets and liabilities:
Increase in interest receivable	2,140	822
Increase in other assets	1,693	(4,567)
Decrease in accrued interest payable	(590)	224
Decrease in accounts payable and accrued expenses	(1,484)	(7,128)
Net cash provided by operating activities	73,033	20,177
Cash flows from investing activities:
Purchases of held-to-maturity investment securities	(934)	(4,870)
Purchases of available-for-sale investment securities	(113,377)	(254,098)
Proceeds from maturities and paydowns of held-to-maturity investment securities	22,751	23,925
Proceeds from maturities and paydowns of available-for-sale investment securities	74,503	153,703
Purchases of company-owned life insurance	0	0
Extensions of credit to customers, net of repayments	35,985	(5,677)
Recoveries of loans charged-off	2,142	3,409
Proceeds from sales of OREO	728	309
Acquisition of banks and bank holding companies, net of cash and cash equivalents received	28,013	0
Capital expenditures, net of sales	(4,456)	(1,408)
Net cash used in investing activities	(10,671)	(84,707)
Cash flows from financing activities:
Net increase (decrease) in deposits	(75,931)	18,526
Net increase (decrease) in repurchase agreements	50,014	(45,112)
Net increase (decrease) in other borrowed funds	(5)	31
Repayments of long-term debt	(17)	(15)
Advances on long-term debt	41	37
Proceeds from issuance of common stock	1,084	996
Excess tax benefits from stock-based compensation	0	307
Purchase and retirement of common stock	(859)	(25,309)
Dividends paid to common stockholders	(10,760)	(9,860)
Net cash provided by (used in) financing activities	(36,433)	(60,399)
Net increase (decrease) in cash and cash equivalents	25,929	(124,929)
Cash and cash equivalents at beginning of period	782,023	780,457
Cash and cash equivalents at end of period	807,952	655,528
Supplemental disclosures of cash flow information:
Cash paid during the period for income taxes	28,750	4,206
Cash paid during the period for interest expense	6,154	15,390
Transfer of loans to other real estate owned	368	3,227
Capitalization of internally originated mortgage servicing rights	$ 1,527	$ 602