Parent Company Condensed Financial Statements (Condensed Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
ASSETS
Cash and cash equivalents due from subsidiary bank	$ 3,001,377	$ 2,174,592	$ 1,878,503	$ 1,360,887
Investments in tax credit and other investments, net	231,635	224,551
Other assets	743,686	650,266
TOTAL	41,042,356	37,121,563	34,788,840
LIABILITIES
Long-term debt	146,835	171,577
Total liabilities	36,618,382	33,279,612
STOCKHOLDERS’ EQUITY
Common stock, $0.001 par value, 200,000,000 shares authorized; 165,867,587 and 165,214,770 shares issued in 2018 and 2017, respectively	166	165
Additional paid-in capital	1,789,811	1,755,330
Retained earnings	3,160,132	2,576,302
Treasury stock, at cost — 20,906,224 shares in 2018 and 20,671,710 shares in 2017	(467,961)	(452,327)
AOCI, net of tax	(58,174)	(37,519)
Total stockholders’ equity	4,423,974	3,841,951	3,427,741	3,122,950
TOTAL	41,042,356	37,121,563
Parent Company
ASSETS
Cash and cash equivalents due from subsidiary bank	149,411	159,566	$ 39,264	$ 18,898
Investments in tax credit and other investments, net	23,259	25,511
Other assets	6,487	7,062
TOTAL	4,584,679	4,026,499
LIABILITIES
Long-term debt	146,835	171,577
Other liabilities	13,870	12,971
Total liabilities	160,705	184,548
STOCKHOLDERS’ EQUITY
Common stock, $0.001 par value, 200,000,000 shares authorized; 165,867,587 and 165,214,770 shares issued in 2018 and 2017, respectively	166	165
Additional paid-in capital	1,789,811	1,755,330
Retained earnings	3,160,132	2,576,302
Treasury stock, at cost — 20,906,224 shares in 2018 and 20,671,710 shares in 2017	(467,961)	(452,327)
AOCI, net of tax	(58,174)	(37,519)
Total stockholders’ equity	4,423,974	3,841,951
TOTAL	4,584,679	4,026,499
Parent Company | Bank
ASSETS
Investments in subsidiaries	4,401,860	3,830,696
Parent Company | Nonbank
ASSETS
Investments in subsidiaries	$ 3,662	$ 3,664