Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Dec. 31, 2017	Jun. 30, 2018
Goodwill [Line Items]
Balance as of beginning of period		$ 2,278,512
Goodwill acquired, net		(9,792)
Impairment		(3,400)
Other		(6,143)
Balance as of end of period	$ 2,278,512	2,259,177
Goodwill	2,708,368	2,692,433
Accumulated impairment losses	(429,856)	(433,256)
CPE
Goodwill [Line Items]
Balance as of beginning of period		1,386,680
Other		(6,143)
Balance as of end of period	1,386,680	1,380,537
Goodwill	1,386,680	1,380,537
N & C
Goodwill [Line Items]
Balance as of beginning of period		573,798
Impairment		(3,400)
Balance as of end of period	573,798	570,398
Goodwill	1,003,654	1,003,654
Accumulated impairment losses	(429,856)	(433,256)
Enterprise
Goodwill [Line Items]
Balance as of beginning of period		318,034
Goodwill acquired, net		(9,792)
Balance as of end of period	318,034	308,242
Goodwill	$ 318,034	$ 308,242