Segment Information - Subcategory Revenues (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenue from External Customer [Line Items]
Sales	$ 177,404	$ 162,125	$ 482,650	$ 480,858
Core Products [Member]
Revenue from External Customer [Line Items]
Sales	158,101	141,035	417,657	400,726
Legacy Products [Member]
Revenue from External Customer [Line Items]
Sales	19,303	21,090	64,993	80,132
Broadband Access (Included in Carrier Systems) [Member] | Core Products [Member]
Revenue from External Customer [Line Items]
Sales	98,132	94,464	251,994	249,988
Optical (Included in Carrier Systems) [Member] | Core Products [Member]
Revenue from External Customer [Line Items]
Sales	16,640	11,160	41,500	39,418
Internetworking (Included in Business Networking) [Member] | Core Products [Member]
Revenue from External Customer [Line Items]
Sales	43,329	35,411	124,163	111,320
HDSL (Does Not Include T1) (Included in Loop Access) [Member] | Legacy Products [Member]
Revenue from External Customer [Line Items]
Sales	11,487	12,926	33,183	51,350
Other Products (Excluding HDSL) [Member] | Legacy Products [Member]
Revenue from External Customer [Line Items]
Sales	$ 7,816	$ 8,164	$ 31,810	$ 28,782