Debt - Guarantees (Details) - 3 months ended Mar. 31, 2017 £ in Millions, CAD in Millions, AUD in Millions	ZAR	AUD guarantee	CAD guarantee	ZAR guarantee	USD ($) guarantee	GBP (£) guarantee
Geo Amey
Line of Credit Facility [Line Items]
Ownership percentage in South African Custodial Services Pty. Limited	50.00%
Working capital line of credit issued to GEOAmey					$ 15,000,000	£ 12.0
Note receivable for GEOAmey					$ 5,600,000	£ 4.5
Ravenhall
Line of Credit Facility [Line Items]
Number of letters of guarantee outstanding under separate international facilities relating to performance guarantees | guarantee		13	13	13	13	13
Letters of credit outstanding relating to performance guarantees					$ 20,200,000
Ravenhall | Letter of Credit | Revolver
Line of Credit Facility [Line Items]
Guaranteed obligations		AUD 100.0			76,400,000
SACS
Line of Credit Facility [Line Items]
Guaranteed obligations				ZAR 7,400,000	600,000
Remaining guarantee under letter of credit | ZAR	ZAR 7,400,000
Maximum loan amount under standby facility				ZAR 20,000,000	1,492,200.0
Amount funded					0
Canada Facility
Line of Credit Facility [Line Items]
Potential estimated exposure of tax obligations			CAD 1.5		$ 1,100,000