Parent Company Only Financial Information, Statement of Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
INCOME
Interest income on notes receivable from subsidiaries	$ 976,990	$ 749,000	$ 659,538
Total income	1,235,148	1,073,900	1,060,156
EXPENSE
Income before income tax expense (benefit) and equity in undistributed net income (loss) of subsidiaries	413,349	338,767	287,596
Income tax expense	79,786	109,503	87,322
Net income	333,562	229,264	200,274
Preferred stock dividends	10,784	9,347	8,903
Net income available to common equity	322,779	219,917	191,371
Parent Company Only
INCOME
Dividends from subsidiaries	336,000	213,000	188,000
Interest income on notes receivable from subsidiaries	12,199	4,175	0
Other income	994	1,763	4,669
Total income	349,193	218,938	192,669
EXPENSE
Interest expense on short and long-term funding	18,355	18,464	21,901
Other expense	11,736	6,927	4,289
Total expense	30,091	25,391	26,190
Income before income tax expense (benefit) and equity in undistributed net income (loss) of subsidiaries	319,102	193,547	166,479
Income tax expense	4,176	4,768	3,468
Income before equity in undistributed net income (loss) of subsidiaries	314,926	188,779	163,011
Equity in undistributed net income (loss) of subsidiaries	18,636	40,485	37,263
Net income	333,562	229,264	200,274
Preferred stock dividends	10,784	9,347	8,903
Net income available to common equity	$ 322,779	$ 219,917	$ 191,371