Segment Reporting - Information about Segment Assets by Country (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total assets	$ 3,200,648	$ 3,222,820
Operating Segments [Member] | AEA [Member]
Segment Reporting Information [Line Items]
Total assets	960,102	921,171
Operating Segments [Member] | MEA [Member]
Segment Reporting Information [Line Items]
Total assets	955,054	1,020,599
Operating Segments [Member] | ASA [Member]
Segment Reporting Information [Line Items]
Total assets	923,226	887,209
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Total assets	$ 362,266	$ 393,841