Goodwill and Other Intangible Assets (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Intangible assets, gross:
Total intangible assets, gross, beginning balance	$ 76,155	$ 76,869
Disposals to total intangible assets, gross		(714)
Total intangible assets, gross, ending balance	76,155	76,155
Intangible assets, accumulated amortization:
Total intangible assets, accumulated amortization, beginning balance	(63,685)	(57,194)
Additions to total intangible assets, accumulated amortization	(5,049)	(6,950)
Disposals to total intangible assets, accumulated amortization		459
Total intangible assets, accumulated amortization, ending balance	(68,734)	(63,685)
Intangible assets, net, beginning balance	12,470	19,675
Disposals to intangible assets, net		(255)
Intangible assets, net, ending balance	7,421	12,470
Publishing Rights
Intangible assets, gross:
Total intangible assets, gross, beginning balance	26,200	26,200
Total intangible assets, gross, ending balance	26,200	26,200
Intangible assets, accumulated amortization:
Total intangible assets, accumulated amortization, beginning balance	(23,438)	(21,495)
Additions to total intangible assets, accumulated amortization	(1,303)	(1,943)
Total intangible assets, accumulated amortization, ending balance	(24,741)	(23,438)
Trademarks
Intangible assets, gross:
Total intangible assets, gross, beginning balance	5,110	5,690
Disposals to total intangible assets, gross		(580)
Total intangible assets, gross, ending balance	5,110	5,110
Intangible assets, accumulated amortization:
Total intangible assets, accumulated amortization, beginning balance	(2,193)	(2,066)
Additions to total intangible assets, accumulated amortization	(419)	(452)
Disposals to total intangible assets, accumulated amortization		325
Total intangible assets, accumulated amortization, ending balance	(2,612)	(2,193)
Customer Relationships
Intangible assets, gross:
Total intangible assets, gross, beginning balance	7,717	7,717
Total intangible assets, gross, ending balance	7,717	7,717
Intangible assets, accumulated amortization:
Total intangible assets, accumulated amortization, beginning balance	(6,478)	(5,779)
Additions to total intangible assets, accumulated amortization	(648)	(699)
Total intangible assets, accumulated amortization, ending balance	(7,126)	(6,478)
Acquired Curriculum and Technology
Intangible assets, gross:
Total intangible assets, gross, beginning balance	24,828	24,828
Total intangible assets, gross, ending balance	24,828	24,828
Intangible assets, accumulated amortization:
Total intangible assets, accumulated amortization, beginning balance	(19,619)	(16,109)
Additions to total intangible assets, accumulated amortization	(2,478)	(3,510)
Total intangible assets, accumulated amortization, ending balance	(22,097)	(19,619)
Reseller Network
Intangible assets, gross:
Total intangible assets, gross, beginning balance	12,300	12,300
Total intangible assets, gross, ending balance	12,300	12,300
Intangible assets, accumulated amortization:
Total intangible assets, accumulated amortization, beginning balance	(11,957)	(11,616)
Additions to total intangible assets, accumulated amortization	(201)	(341)
Total intangible assets, accumulated amortization, ending balance	$ (12,158)	(11,957)
Conference Attendees
Intangible assets, gross:
Total intangible assets, gross, beginning balance		134
Disposals to total intangible assets, gross		(134)
Intangible assets, accumulated amortization:
Total intangible assets, accumulated amortization, beginning balance		(129)
Additions to total intangible assets, accumulated amortization		(5)
Disposals to total intangible assets, accumulated amortization		$ 134