Financial Instruments (Details 6) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value of long-term debt		$ 834,600		$ 885,000
Carrying value of long-term debt		880,835		854,897
Unit adjustment liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of year		93,762		106,343
Payments		(22,320)		(22,320)
Change in fair value to the unit adjustment liability		8,491		9,740
Balance at end of year		79,934	[1]	93,762
Contingent Consideration for Acquisition [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of year	[1]	$ 93,762
Balance at end of year	[1]			$ 93,762

[1] Does not total due to rounding.