Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities:
Net income	$ 20,124	$ 20,980
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	4,000	1,095
Net (gain) loss on disposal of property and equipment	142	(204)
Depreciation and amortization	4,679	4,544
Net premium amortization on investment securities	3,238	3,684
Net gains on investment securities transactions	21	(6)
Net gains on sales of mortgage loans held for sale	(4,588)	(4,321)
Net gain on sale of OREO	(102)	(750)
Write-downs of OREO and other assets pending disposal	17	106
Net reversal of impairment of mortgage servicing rights	15	(15)
Deferred income tax expense	(517)	4,914
Net increase in cash surrender value of company-owned life insurance policies	(1,143)	(920)
Stock-based compensation expense	955	832
Tax benefits from stock-based compensation expense	420	480
Excess tax benefits from stock-based compensation	(307)	(292)
Originations of loans held for sale	(195,444)	(239,527)
Proceeds from sales of loans held for sale	199,316	228,259
Changes in operating assets and liabilities:
Increase in interest receivable	822	(179)
Increase in other assets	(4,567)	(3,630)
Decrease in accrued interest payable	224	(720)
Decrease in accounts payable and accrued expenses	(7,128)	(15,682)
Net cash provided by operating activities	20,177	(1,352)
Cash flows from investing activities:
Purchases of held-to-maturity investment securities	(4,870)	(11,733)
Purchases of available-for-sale investment securities	(254,098)	(153,953)
Proceeds from maturities and paydowns of held-to-maturity investment securities	23,925	22,826
Proceeds from maturities and paydowns of available-for-sale investment securities	153,703	95,996
Extensions of credit to customers, net of repayments	(5,677)	(20,050)
Recoveries of loans charged-off	3,409	1,901
Proceeds from sales of OREO	309	2,321
Capital expenditures, net of sales	(1,408)	(382)
Net cash used in investing activities	(84,707)	(63,074)
Cash flows from financing activities:
Net increase (decrease) in deposits	18,526	(38,053)
Net increase (decrease) in repurchase agreements	(45,112)	(40,177)
Net increase (decrease) in other borrowed funds	31	(5)
Repayments of long-term debt	(15)	(15)
Advances on long-term debt	37	4,996
Proceeds from issuance of common stock	996	900
Excess tax benefits from stock-based compensation	307	292
Purchase and retirement of common stock	(25,309)	(15,264)
Dividends paid to common stockholders	(9,860)	(9,115)
Net cash provided by (used in) financing activities	(60,399)	(96,441)
Net increase (decrease) in cash and cash equivalents	(124,929)	(160,867)
Cash and cash equivalents at beginning of period	780,457	798,670
Cash and cash equivalents at end of period	655,528	637,803
Supplemental disclosures of cash flow information:
Cash paid during the period for income taxes	4,206	5,100
Cash paid during the period for interest expense	15,390	5,187
Transfer of loans to other real estate owned	3,227	3,257
Capitalization of internally originated mortgage servicing rights	$ 602	$ 659