Selected Segment Financial Data, Revenues and Long lived Assets (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Revenues	$ 326,395	$ 225,735	$ 240,599	$ 231,462	$ 342,730	$ 216,975	$ 219,930	$ 226,066	$ 1,024,191	$ 1,005,701	$ 1,045,977
Long lived assets
Long lived assets	1,373,069				1,416,825				1,373,069	1,416,825
United States [Member]
Revenues
Revenues									541,235	527,431	628,013
Long lived assets
Long lived assets	759,513				752,442				759,513	752,442
Other [Member]
Revenues
Revenues									482,956	478,270	$ 417,964
Long lived assets
Long lived assets	$ 613,556				$ 664,383				$ 613,556	$ 664,383