Commitments and Contingencies - Colombia-Related - Tort Lawsuits (Details) (USD $)	3 Months Ended		12 Months Ended	1 Months Ended	46 Months Ended	37 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2007 count	Nov. 30, 2012 lawsuit	Mar. 31, 2011 lawsuit	Mar. 31, 2011 lawsuit	Feb. 28, 2010 lawsuit
Loss Contingencies [Line Items]
Interest income	$ 664,000	$ 664,000
Colombia | ATS lawsuits
Loss Contingencies [Line Items]
Number of lawsuits plead or dismissed after the parties reached a confidential settlement agreement			1
Colombia | ATA lawsuits
Loss Contingencies [Line Items]
Number of lawsuits plead or dismissed after the parties reached a confidential settlement agreement				1
Number of lawsuits for which the motion to dismiss was granted in part and denied in part							1
Colombia | Pending litigation | ATS lawsuits
Loss Contingencies [Line Items]
Number of new claims filed					9
Colombia | Pending litigation | ATS lawsuits | Minimum
Loss Contingencies [Line Items]
Minimum number of alleged victims	6,000
Colombia | Pending litigation | Unspecified compensatory and punitive damages and attorney's fees and costs
Loss Contingencies [Line Items]
Number of pending lawsuits	8
Colombia | Pending litigation | Treble damages and disgorgement of profits without explanation
Loss Contingencies [Line Items]
Number of pending lawsuits	1
Colombia | Pending litigation | Specific demand
Loss Contingencies [Line Items]
Specific demand for compensatory damages	10,000,000
Specific demand for punitive damages	$ 10,000,000
Colombia | Pending litigation | ATA lawsuits
Loss Contingencies [Line Items]
Number of new claims filed						4