Commitments and Contingencies - Colombia-Related Matters - Insurance Recovery (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2013 insurer	Sep. 30, 2015 USD ($) insurer	Sep. 30, 2014 USD ($) insurer	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2008 insurer	Dec. 31, 2009 insurer
Gain Contingencies [Line Items]
Interest income | $		$ 607	$ 600	$ 1,909	$ 1,905
Colombia | Insurance recovery coverage suit
Gain Contingencies [Line Items]
Initial number of primary general liability insurers involved in coverage suit			1			3
Number of primary insurers with which the company reached settlement agreements							3
Percent of defense costs in the ATA and ATS lawsuits to be paid by primary insurers							40.00%
Expense reimbursement received to date which is deferred in Other liabilities | $				12,000
Interest income | $				$ 2,000
Colombia | Two insurers who had been placed in liquidation
Gain Contingencies [Line Items]
Initial number of primary general liability insurers involved in coverage suit	2
Percent of defense costs in the ATA and ATS lawsuits to be paid by primary insurers							1.00%
Colombia | Defendant seeking a declaratory judgment relieving coverage obligation
Gain Contingencies [Line Items]
Initial number of primary general liability insurers involved in coverage suit		1
Percent of defense costs in the ATA and ATS lawsuits to be paid by primary insurers							40.00%