Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Cash flows from operating activities:
Net income	$ 20,980	$ 21,393
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	1,095	(5,000)
Net (gain) loss on disposal of property and equipment	(204)	(13)
Depreciation and amortization	4,544	3,896
Net premium amortization on investment securities	3,684	3,371
Net gains on investment securities transactions	(6)	(71)
Net gains on sales of mortgage loans held for sale	(4,321)	(3,323)
Net gain on sale of OREO	(750)	(435)
Write-downs of OREO and other assets pending disposal	106	0
Net reversal of impairment of mortgage servicing rights	(15)	(45)
Deferred income tax expense	4,914	2,630
Net increase in cash surrender value of company-owned life insurance policies	(920)	(852)
Stock-based compensation expense	832	712
Tax benefits from stock-based compensation expense	480	989
Excess tax benefits from stock-based compensation	(292)	(982)
Originations of loans held for sale	(239,527)	(151,911)
Proceeds from sales of loans held for sale	228,259	157,141
Changes in operating assets and liabilities:
Increase in interest receivable	(179)	(685)
Increase in other assets	(3,630)	(1,083)
Decrease in accrued interest payable	(720)	(10)
Decrease in accounts payable and accrued expenses	(15,682)	(3,694)
Net cash provided by operating activities	(1,352)	22,028
Cash flows from investing activities:
Purchases of held-to-maturity investment securities	(11,733)	0
Purchases of available-for-sale investment securities	(153,953)	(95,077)
Proceeds from maturities and paydowns of held-to-maturity investment securities	22,826	2,185
Proceeds from maturities and paydowns of available-for-sale investment securities	95,996	160,337
Purchases of company-owned life insurance	0	(15,000)
Proceeds from sales of mortgage servicing rights	0	266
Extensions of credit to customers, net of repayments	(20,050)	(28,580)
Recoveries of loans charged-off	1,901	3,822
Proceeds from sales of OREO	2,321	2,760
Capital expenditures, net of sales	(382)	(3,142)
Net cash used in investing activities	(63,074)	27,571
Cash flows from financing activities:
Net increase (decrease) in deposits	(38,053)	1,387
Net increase (decrease) in repurchase agreements	(40,177)	31,461
Net increase (decrease) in other borrowed funds	(5)	6
Repayments of long-term debt	(15)	(12)
Advances on long-term debt	4,996	0
Proceeds from issuance of common stock	900	2,476
Excess tax benefits from stock-based compensation	292	982
Purchase and retirement of common stock	(15,264)	(3,159)
Dividends paid to common stockholders	(9,115)	(7,036)
Net cash provided by (used in) financing activities	(96,441)	26,105
Net increase (decrease) in cash and cash equivalents	(160,867)	75,704
Cash and cash equivalents at beginning of period	798,670	534,827
Cash and cash equivalents at end of period	637,803	610,531
Supplemental disclosures of cash flow information:
Cash paid during the period for income taxes	5,100	0
Cash paid during the period for interest expense	$ 5,187	$ 4,561