Derivative Financial Instruments - Summary of Derivative Positions (Details) - 9 months ended Sep. 30, 2018	USD ($) € / £ $ / £	GBP (£) € / £ $ / £
USD/British Pound | Sell
Derivative [Line Items]
Notional Amount		£ 1,962,900
Weighted Average Remaining Maturity In Years	3 months 19 days
Average Exchange Rate | $ / £	1.31	1.31
EURO/British Pound | Sell
Derivative [Line Items]
Notional Amount		£ 2,568,300
Weighted Average Remaining Maturity In Years	3 months 19 days
Average Exchange Rate | € / £	1.12	1.12
Interest Rate Swaps
Derivative [Line Items]
Notional Amount | $	$ 216,562,500
Weighted Average Remaining Maturity In Years	4 years 3 months