Accumulated Other Comprehensive Income ("AOCI") (AOCI by component) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, value	$ 5,007,701	$ 7,618,496
Cumulative effect of accounting change (see Note 3)			$ 14,519
Ending balance, value	5,024,878	7,563,327
Interest rate swaps
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, value	23,542	8,066
Cumulative effect of accounting change (see Note 3)	2,851
OCI before reclassifications	10,258	5,842
Amounts reclassified from AOCI	0	0
Net current period OCI	10,258	5,842
Ending balance, value	36,651	13,908
Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, value	128,682	118,972
Cumulative effect of accounting change (see Note 3)	(108,374)		$ (108,374)
OCI before reclassifications	9,950	(9,221)
Amounts reclassified from AOCI	0	9,268
Net current period OCI	9,950	47
Ending balance, value	30,258	119,019
Securities available for sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, value	109,554	130,505
Cumulative effect of accounting change (see Note 3)	(109,554)
OCI before reclassifications	0	(15,009)
Amounts reclassified from AOCI	0	0
Net current period OCI	0	(15,009)
Ending balance, value	0	115,496
Pro-rata share of nonconsolidated subsidiaries' OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, value	3,769	(12,058)
Cumulative effect of accounting change (see Note 3)	(1,671)
OCI before reclassifications	346	(51)
Amounts reclassified from AOCI	0	9,268
Net current period OCI	346	9,217
Ending balance, value	2,444	(2,841)
Other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, value	(8,183)	(7,541)
Cumulative effect of accounting change (see Note 3)	0
OCI before reclassifications	(654)	(3)
Amounts reclassified from AOCI	0	0
Net current period OCI	(654)	(3)
Ending balance, value	$ (8,837)	$ (7,544)