Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 74,033	$ 80,311	$ 65,999	$ 78,972
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of investment premiums, net	1,829			5,907
Gain on sale of other real estate owned, net	(110)			(43)
Valuation adjustment on other real estate owned	59			5
Provision for loan and lease losses	13,684			13,656
Change in cash surrender value of bank owned life insurance	(2,135)			(2,105)
Depreciation, amortization and accretion	11,554			13,943
Gain on sale of premises and equipment	(195)			(1,341)
Gain on store divestiture	(1,225)			0
Additions to residential mortgage servicing rights carried at fair value	(3,887)			(6,530)
Change in fair value of residential mortgage servicing rights carried at fair value	13,966			(5,079)
Gain on redemption of junior subordinated debentures at amortized cost	0			(1,043)
Stock-based compensation	754			1,829
Net increase in equity and other investments	(791)			(107)
Unrealized holding gains on equity securities	(695)			0
Gain on sale of loans, net	(13,025)			(14,508)
Change in fair value of loans held for sale	(2,793)			306
Origination of loans held for sale	(487,090)			(687,226)
Proceeds from sales of loans held for sale	428,298			659,977
Change in other assets and liabilities:
Net (increase) decrease in other assets	(56,976)			10,116
Net (decrease) increase in other liabilities	(28,872)			2,261
Net cash (used in) provided by operating activities	(53,617)			68,990
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of investment securities available for sale	(5,953)			(89,145)
Proceeds from investment securities available for sale	119,381			107,908
Proceeds from investment securities held to maturity	174			172
Purchases of restricted equity securities	(205,400)			0
Redemption of restricted equity securities	198,202			7
Net change in loans and leases	(23,868)			(276,481)
Proceeds from sales of loans	15,848			21,629
Change in premises and equipment	(2,365)			(462)
Proceeds from bank owned life insurance death benefits	1,550			0
Proceeds from sales of other real estate owned	616			161
Net cash paid in store divestiture	(44,646)			0
Net cash provided by (used in) investing activities	53,539			(236,211)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net increase in deposit liabilities	155,937			158,771
Net decrease in securities sold under agreements to repurchase	(8,207)			(2,315)
Proceeds from term debt borrowings	230,670			50,000
Repayment of term debt borrowings	(50,000)			(50,513)
Repayment of junior subordinated debentures at amortized cost	0			(10,598)
Dividends paid on common stock	(46,254)			(39,634)
Proceeds from stock options exercised	21			759
Repurchase and retirement of common stock	(1,918)			(4,340)
Net cash provided by financing activities	280,249			102,130
Net increase (decrease) in cash and cash equivalents	280,171			(65,091)
Cash and cash equivalents, beginning of period	622,637		$ 569,189	634,280
Cash and cash equivalents, end of period	902,808	$ 622,637		569,189
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Interest	44,026			23,489
Income taxes	34,383			11,440
SUPPLEMENTAL DISCLOSURE OF NONCASH INVESTING AND FINANCING ACTIVITIES:
Change in unrealized gains on investment securities available for sale, net of taxes	24,712			(31,419)
Change in unrealized gains on junior subordinated debentures carried at fair value, net of taxes	4,920			(1,253)
Junior subordinated debentures, at fair value, cumulative effect adjustment	0			9,710
Cash dividend declared on common stock and payable after period-end	46,297			44,016
Change in GNMA mortgage loans recognized due to repurchase option	(8,760)			(6,152)
Transfer of loans to other real estate owned	95			1,444
Change in receivable from BOLI death benefits	$ (92)			$ 1,224