Revenues Based on Location of Legal Entity (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 441,920	$ 438,042	$ 460,147	$ 470,285	$ 442,204	$ 455,470	$ 449,137	$ 432,338	$ 1,810,394	$ 1,779,149	$ 1,756,212
UNITED STATES
Segment Reporting Information [Line Items]
Revenues									1,298,492	1,281,444	1,256,046
UNITED KINGDOM
Segment Reporting Information [Line Items]
Revenues									246,236	236,925	232,281
All Other Foreign Countries
Segment Reporting Information [Line Items]
Revenues									$ 265,666	$ 260,780	$ 267,885