Other Comprehensive Income (Loss) (Amounts Included in Accumulated Other Comprehensive Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Components of Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ (5,593)	$ (1,869)
Amounts reclassified into earnings			2,074	818
Changes in fair value			(4,078)	(1,429)
Ending balance	$ (7,597)	$ (2,480)	(7,597)	(2,480)
Interest Rate Swap [Member]
Components of Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(4,372)	(3,226)
Amounts reclassified into earnings	639	546	1,277	1,205
Changes in fair value	639	(1,362)	(2,735)	(1,539)
Ending balance	(5,830)	(3,560)	(5,830)	(3,560)
Fuel [Member] | Commodity Contract [Member]
Components of Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(1,221)	1,357
Amounts reclassified into earnings	417	(187)	797	(387)
Changes in fair value	(1,024)	287	(1,343)	110
Ending balance	$ (1,767)	$ 1,080	$ (1,767)	$ 1,080