Parent Company Only Financial Information, Statement of Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income
Interest income on notes receivable from subsidiaries	$ 785,241	$ 998,099	$ 976,990
Total income	1,277,012	1,216,498	1,235,148
Expense
Income before income tax expense	326,972	406,509	413,349
Income tax expense	20,200	79,720	79,786
Net income	306,771	326,790	333,562
Preferred stock dividends	18,358	15,202	10,784
Net income available to common equity	288,413	311,587	322,779
Parent Company Only
Income
Income from subsidiaries	317,895	341,789	354,637
Interest income on notes receivable from subsidiaries	3,257	13,983	12,199
Other income	933	761	994
Total income	322,084	356,532	367,830
Expense
Interest expense on short and long-term funding	10,960	16,802	18,355
Other expense	6,422	6,583	11,736
Total expense	17,383	23,384	30,091
Income before income tax expense	304,702	333,148	337,739
Income tax expense	(2,070)	6,359	4,176
Net income	306,771	326,790	333,562
Preferred stock dividends	18,358	15,202	10,784
Net income available to common equity	$ 288,413	$ 311,587	$ 322,779