Derivative Financial Instruments - Fair Value of Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives		$ 818	$ 87,531
Fair value of liability derivatives		7,063	77,826
Proceeds (payments) to terminate and or amend derivative instruments		(30,400)	4,000
Interest Rate Cap [Member]
Derivatives, Fair Value [Line Items]
Proceeds (payments) to terminate and or amend derivative instruments	$ 913
Derivative Financial Instruments, Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives		818	87,531
Derivative Financial Instruments, Assets [Member] | 1:3 basis swaps [Member]
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives		0	0
Proceeds (payments) to terminate and or amend derivative instruments		2,100	600
Derivative Financial Instruments, Assets [Member] | Interest rate swaps - floor income hedges [Member]
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives		0	81,159
Proceeds (payments) to terminate and or amend derivative instruments			3,400
Derivative Financial Instruments, Assets [Member] | Interest rate swap option - floor income hedge [Member]
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives		543	2,977
Derivative Financial Instruments, Assets [Member] | Interest rate swaps - hybrid debt hedges [Member]
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives		0	0
Derivative Financial Instruments, Assets [Member] | Interest Rate Cap [Member]
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives		275	1,152
Proceeds (payments) to terminate and or amend derivative instruments		900
Derivative Financial Instruments, Assets [Member] | Cross-currency interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives		0	0
Proceeds (payments) to terminate and or amend derivative instruments		(33,400)
Derivative Financial Instruments, Assets [Member] | Other [Member]
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives		0	2,243
Derivative Financial Instruments, Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of liability derivatives		7,063	77,826
Derivative Financial Instruments, Liabilities [Member] | 1:3 basis swaps [Member]
Derivatives, Fair Value [Line Items]
Fair value of liability derivatives		0	2,624
Derivative Financial Instruments, Liabilities [Member] | Interest rate swaps - floor income hedges [Member]
Derivatives, Fair Value [Line Items]
Fair value of liability derivatives		0	256
Derivative Financial Instruments, Liabilities [Member] | Interest rate swap option - floor income hedge [Member]
Derivatives, Fair Value [Line Items]
Fair value of liability derivatives		0	0
Derivative Financial Instruments, Liabilities [Member] | Interest rate swaps - hybrid debt hedges [Member]
Derivatives, Fair Value [Line Items]
Fair value of liability derivatives		7,063	7,341
Derivative Financial Instruments, Liabilities [Member] | Interest Rate Cap [Member]
Derivatives, Fair Value [Line Items]
Fair value of liability derivatives		0	0
Derivative Financial Instruments, Liabilities [Member] | Cross-currency interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Fair value of liability derivatives		0	67,605
Derivative Financial Instruments, Liabilities [Member] | Other [Member]
Derivatives, Fair Value [Line Items]
Fair value of liability derivatives		$ 0	$ 0