Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Accrued expenses
Salaries, bonuses and benefits	$ 9,383	$ 6,439
Accrued interest		5,119
Accrued royalties	1,201	1,369
Pension and post-retirement benefit plans	1,093	1,173
Headsprout acquisition accrual		400
Other	2,547	2,932
Accrued expenses	$ 14,224	$ 17,432