Income Taxes - Deferred tax liabilities and deferred tax assets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax liabilities:
Deferred sales commissions	$ (484)	$ (2,337)
Property and equipment	(13,906)	(9,775)
Benefit plans	(12,137)	(14,058)
Identifiable intangible assets	(11,118)	(13,705)
Prepaid expenses	(1,968)	(2,231)
Total gross deferred liabilities	(39,613)	(42,106)
Deferred tax assets:
Accrued compensation	10,678	11,015
Additional pension and postretirement liability	27,204	32,183
Other accrued expenses	7,058	5,851
Unrealized losses on investment securities and partnerships	1,834	7,426
Capital loss carryforwards	3,920	5,919
Nonvested stock	20,516	20,608
Unused state tax credits	2,115	1,470
State net operating loss carryforwards	5,716	5,666
Other	3,430	3,463
Total gross deferred assets	82,471	93,601
Valuation allowance	(11,428)	(18,803)
Net deferred tax asset	31,430	32,692
Capital loss carryforward, valuation allowance	5,800	13,300
Operating loss carryforward, valuation allowance	5,600	$ 5,500
State tax credit carryforwards that will expire between 2024 and 2032 if not utilized	1,900
State tax credit carryforwards that will expire in 2026 if not utilized	$ 200