Derivative Financial Instruments - Income Statement Effect of Derivative Instruments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Derivative settlements, net	$ 667	$ (21,949)	$ (24,250)
Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative settlements, net	667	(21,949)	(24,250)
Change in fair value	26,379	59,895	(15,150)
Re-measurement of Euro Notes (foreign currency transaction adjustment) - income (expense)	(45,600)	11,849	43,801
Derivative market value and foreign currency transaction adjustments and derivative settlements, net - income (expense)	(18,554)	49,795	4,401
1:3 basis swaps [Member] | Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative settlements, net	(3,069)	1,493	1,058
Change in fair value	(8,224)	(2,938)	12,292
Interest rate swaps - floor income hedges [Member] | Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative settlements, net	10,838	(17,643)	(23,041)
Change in fair value	3,585	64,111	20,103
Interest rate swap option - floor income hedges [Member] | Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in fair value	(2,433)	(281)	(2,420)
Interest rate swaps - hybrid debt hedges [Member] | Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative settlements, net	(781)	(915)	(1,012)
Change in fair value	279	304	(295)
Interest Rate Cap [Member] | Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in fair value	(893)	(419)	(1,365)
Cross-currency interest rate swaps [Member] | Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative settlements, net	(6,321)	(4,884)	(1,255)
Change in fair value	34,208	(1,954)	(45,195)
Other [Member] | Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in fair value	$ (143)	$ 1,072	$ 1,730