Derivative Financial Instruments - Impact on Interest Expense of Interest Rate Agreements Accounted for as Cash Flow Hedges (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Total interest expense	$ (20,537)	$ (21,597)	$ (22,444)	$ (23,950)	$ (25,039)	$ (23,875)	$ (23,008)	$ (23,961)	$ (88,528)	$ (95,883)	$ (87,463)
Cash Flow Hedging | Interest Rate Contract
Derivative [Line Items]
Net interest expense on cash flows hedges									(5,317)	(5,883)	(5,951)
Realized net losses reclassified from other comprehensive income									(72)	(95)	(164)
Total interest expense									$ (5,389)	$ (5,978)	$ (6,115)