Commitments and Contingencies - Colombia-Related - Tort Lawsuits (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended	37 Months Ended	46 Months Ended
	Nov. 30, 2012 lawsuit	Sep. 30, 2015 USD ($) lawsuit	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) lawsuit plaintiff	Sep. 30, 2014 USD ($)	Dec. 31, 2007 count	Mar. 31, 2011 lawsuit	Mar. 31, 2011 lawsuit	Feb. 28, 2010 lawsuit
Loss Contingencies [Line Items]
Interest income | $		$ 607	$ 600	$ 1,909	$ 1,905
Colombia | ATS lawsuits
Loss Contingencies [Line Items]
Number of lawsuits plead or dismissed after the parties reached a confidential settlement agreement | count						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 | plaintiff				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		8
Colombia | Pending litigation | Treble damages and disgorgement of profits without explanation
Loss Contingencies [Line Items]
Number of pending lawsuits		1		1
Colombia | Pending litigation | Specific demand
Loss Contingencies [Line Items]
Specific demand for compensatory damages | $		$ 10,000		$ 10,000
Specific demand for punitive damages | $		$ 10,000		$ 10,000
Colombia | Pending litigation | ATA lawsuits
Loss Contingencies [Line Items]
Number of new claims filed							4