Stockholders' Equity - Reclassifications out of Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
General and Administrative Expense	$ (22,808)	$ (23,704)	$ (20,881)
Amounts reclassified from accumulated other comprehensive income (loss)	(720)	191
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	(720)
Prior service costs | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
General and Administrative Expense	(1,189)
Actuarial loss | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
General and Administrative Expense	$ 469