Pension and Other Retirement Plans - Amounts Recognized in Consolidated Balance Sheets (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Employee compensation and benefits (1)	[1]	$ 0	$ 0
Pension obligations, net (2)	[2]	(396,875)	(444,401)
Postretirement medical, life and other benefits (2)	[2]	0	0
Net amount recognized		(396,875)	(444,401)
Other Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Employee compensation and benefits (1)	[1]	(1,157)	(1,324)
Pension obligations, net (2)	[2]	0	0
Postretirement medical, life and other benefits (2)	[2]	(6,517)	(7,551)
Net amount recognized		$ (7,674)	$ (8,875)

[1] (1)Included in current liabilities within the Company’s Consolidated Balance Sheets.

[2] (2)Included in non-current liabilities within the Company’s Consolidated Balance Sheets.