Other Comprehensive Loss - Changes in Accumulated OCI by Component (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 3,246,012	$ 3,463,469	$ 3,797,528
Other comprehensive income (loss) before reclassifications	2,258	1,403	(104)
Change in cash flow hedges reclassed to earnings	828	688	1,173
Total other comprehensive income	3,377	2,210	288
Ending Balance	2,897,438	3,246,012	3,463,469
Net current-period other comprehensive income (loss)	3,086	2,091	1,069
Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(3,930)	(6,109)	(8,485)
Other comprehensive income (loss) before reclassifications	1,002	1,491	1,203
Change in cash flow hedges reclassed to earnings	828	688	1,173
Total other comprehensive income	1,830	2,179	2,376
Ending Balance	(2,100)	(3,930)	(6,109)
Foreign Currency Items [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(262)	(174)	1,133
Other comprehensive income (loss) before reclassifications	1,256	(88)	(1,307)
Change in cash flow hedges reclassed to earnings	0	0	0
Total other comprehensive income	1,256	(88)	(1,307)
Ending Balance	994	(262)	(174)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(4,192)	(6,283)	(7,352)
Ending Balance	$ (1,106)	$ (4,192)	$ (6,283)