Schedule of Interest Rate Swap Agreements on Accumulated Other Comprehensive Income (Details) - Interest Rate Swap - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Beginning balance	$ (30,042)	$ (111,174)	$ (243,051)
Unrealized gain on interest rate swaps			15,030
Reclassification of net losses included in income statement	30,715	81,132	116,847
Ending balance	$ 673	$ (30,042)	$ (111,174)