Parent Company Only Financial Information, Statement of Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
INCOME
Interest income on notes receivable	$ 615,627	$ 598,582	$ 587,526
Total income	1,004,687	971,286	958,642
EXPENSE
Income before income taxes	269,788	276,045	267,893
Income tax expense	81,487	85,536	79,201
Net income	188,301	190,509	188,692
Preferred stock dividends	(7,155)	(5,002)	(5,158)
Net income available to common equity	181,146	185,507	183,534
Parent Company [Member]
INCOME
Dividends from subsidiaries	205,000	223,000	262,000
Interest income on notes receivable	0	1,264	1,988
Other income	8,441	9,682	7,742
Total income	213,441	233,946	271,730
EXPENSE
Interest expense on short and long-term funding	39,576	24,847	27,167
Other expense	4,684	745	8,029
Total expense	(44,260)	(25,592)	(35,196)
Income before income taxes	169,181	208,354	236,534
Income tax expense	(1,665)	(5,801)	(7,086)
Income before equity in undistributed net income (loss) of subsidiaries	170,846	214,155	243,620
Equity in undistributed net income (loss) of subsidiaries	17,455	(23,646)	(54,928)
Net income	188,301	190,509	188,692
Preferred stock dividends	(7,155)	(5,002)	(5,158)
Net income available to common equity	$ 181,146	$ 185,507	$ 183,534