Parent Company Only Financial Statements Parent Company Only Financial Statements, Condensed Balance Sheet Statement (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets [Abstract]
Cash and cash equivalents	$ 1,143,424	$ 2,317,054	$ 2,537,497	$ 2,643,599
Available for sale securities	8,857,120	8,321,578
Loan to bank subsidiary	21,449,273	16,922,742
Other assets	446,891	359,092
Total assets	38,020,504	32,272,160
Liabilities [Abstract]
Other liabilities	183,480	162,381
Subordinated debentures	275,913	144,677
Total liabilities	33,577,459	28,753,826
Shareholders' equity: [Abstract]
Common stock	5	4
Capital surplus	1,334,030	1,035,895
Retained earnings	3,369,654	3,048,487
Treasury stock	(198,995)	(552,845)
Accumulated other comprehensive loss	(72,585)	(36,174)	(10,967)	21,587
Total shareholders’ equity	4,432,109	3,495,367
Total liabilities and shareholders’ equity	38,020,504	32,272,160
Parent Company [Member]
Assets [Abstract]
Cash and cash equivalents	167,093	205,876	$ 163,418	$ 282,169
Available for sale securities	0	16,185
Loan to bank subsidiary	65,228	0
Investment in bank subsidiaries	4,236,654	3,255,912
Investment in non-bank subsidiaries	218,007	170,966
Other assets	32,999	4,065
Total assets	4,719,981	3,653,004
Liabilities [Abstract]
Other liabilities	11,959	12,960
Subordinated debentures	275,913	144,677
Total liabilities	287,872	157,637
Shareholders' equity: [Abstract]
Common stock	5	4
Capital surplus	1,334,030	1,035,895
Retained earnings	3,369,654	3,048,487
Treasury stock	72,585	36,174
Accumulated other comprehensive loss	(198,995)	(552,845)
Total shareholders’ equity	4,432,109	3,495,367
Total liabilities and shareholders’ equity	$ 4,719,981	$ 3,653,004