Accumulated Other Comprehensive Income ("AOCI") (AOCI by component) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 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	$ 4,943,587	$ 7,644,230	4,943,587	7,644,230
Interest rate swaps
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, value	36,651	13,908	23,542	8,066
Cumulative effect of accounting change (see Note 3)					2,851
OCI before reclassifications	2,908	(1,206)	13,166	4,636
Amounts reclassified from AOCI	0	0	0	0
Net current period OCI	2,908	(1,206)	13,166	4,636
Ending balance, value	39,559	12,702	39,559	12,702
Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, value	30,258	119,019	128,682	118,972
Cumulative effect of accounting change (see Note 3)					(108,374)
OCI before reclassifications	3,093	(3,180)	13,043	(12,401)
Amounts reclassified from AOCI	0	0	0	9,268
Net current period OCI	3,093	(3,180)	13,043	(3,133)
Ending balance, value	33,351	115,839	33,351	115,839
Securities available for sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, value	0	115,496	109,554	130,505
Cumulative effect of accounting change (see Note 3)					(109,554)
OCI before reclassifications	0	(1,206)	0	(16,215)
Amounts reclassified from AOCI	0	0	0	0
Net current period OCI	0	(1,206)	0	(16,215)
Ending balance, value	0	114,290	0	114,290
Pro-rata share of nonconsolidated subsidiaries' OCI
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, value	2,444	(2,841)	3,769	(12,058)
Cumulative effect of accounting change (see Note 3)					(1,671)
OCI before reclassifications	390	(980)	736	(1,031)
Amounts reclassified from AOCI	0	0	0	9,268
Net current period OCI	390	(980)	736	8,237
Ending balance, value	2,834	(3,821)	2,834	(3,821)
Other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, value	(8,837)	(7,544)	(8,183)	(7,541)
Cumulative effect of accounting change (see Note 3)					$ 0
OCI before reclassifications	(205)	212	(859)	209
Amounts reclassified from AOCI	0	0	0	0
Net current period OCI	(205)	212	(859)	209
Ending balance, value	$ (9,042)	$ (7,332)	$ (9,042)	$ (7,332)