Derivative Financial Instruments (Details) £ in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($)	Mar. 31, 2016 GBP (£) item	Mar. 31, 2016 USD ($) item
Derivative
Gains or losses recorded to accumulated other comprehensive loss reclassified to earnings	$ 0
Reclassification out of Accumulated Other Comprehensive Income
Effects of Change in Interest Rates
Reclassification of unrealized gains into other income (expense), ineffectiveness	100
Interest rate swap, entered in July 2005, maturity in July 2020
Effects of Change in Interest Rates
+50 Basis Points	1,066
-50 Basis Points	(773)
+100 Basis Points	1,986
-100 Basis Points	(1,692)
Interest rate swap, entered in July 2005, maturity in July 2020 | BMA Swap Index
Derivative
Notional amount			$ 45,600
Fair value of hedge, liabilities			$ (5,487)
Interest rate swap, entered in July 2005, maturity in July 2020 | Cash flow hedge
Derivative
Number of interest-rate swap contracts | item		3	3
Interest rate swap, entered in July 2005, maturity in July 2020 | Cash flow hedge | BMA Swap Index
Derivative
Fixed Rate/Buy Amount (as a percent)		3.82%	3.82%
Interest rate swap, entered in November 2008, maturity in October 2016
Effects of Change in Interest Rates
+50 Basis Points	67
-50 Basis Points	(68)
+100 Basis Points	135
-100 Basis Points	(135)
Interest rate swap, entered in November 2008, maturity in October 2016 | LIBOR
Derivative
Notional amount			$ 24,900
Fair value of hedge, liabilities			$ (532)
Interest rate swap, entered in November 2008, maturity in October 2016 | Cash flow hedge | LIBOR
Derivative
Fixed Rate/Buy Amount (as a percent)		5.95%	5.95%
Floating/Exchange Rate Index, percentage		1.50%	1.50%
Interest rate swap, entered in July 2012, maturity in June 2016
Effects of Change in Interest Rates
+50 Basis Points	209
-50 Basis Points	(200)
+100 Basis Points	417
-100 Basis Points	(401)
Interest rate swap, entered in July 2012, maturity in June 2016 | GBP LIBOR
Derivative
Notional amount | £		£ 137,000
Fair value of hedge, liabilities			$ (29)
Interest rate swap, entered in July 2012, maturity in June 2016 | Cash flow hedge
Derivative
Buy (sell) amount | £		£ 7,200
Interest rate swap, entered in July 2012, maturity in June 2016 | Cash flow hedge | GBP LIBOR
Derivative
Fixed Rate/Buy Amount (as a percent)		1.81%	1.81%
Floating/Exchange Rate Index, percentage		1.20%	1.20%
Interest rate swap, entered in January 2015, maturity in October 2017
Effects of Change in Interest Rates
+50 Basis Points	2,486
-50 Basis Points	(2,494)
+100 Basis Points	4,976
-100 Basis Points	(4,984)
Interest rate swap, entered in January 2015, maturity in October 2017 | GBP LIBOR
Derivative
Notional amount | £		£ 220,000
Fair value of hedge, liabilities			$ (1,336)
Interest rate swap, entered in January 2015, maturity in October 2017 | Cash flow hedge
Derivative
Exchange rate GBP/USD		1.5149	1.5149
Interest rate swap, entered in January 2015, maturity in October 2017 | Cash flow hedge | GBP LIBOR
Derivative
Fixed Rate/Buy Amount (as a percent)		1.79%	1.79%
Floating/Exchange Rate Index, percentage		0.975%	0.975%
Currency swap, entered in July 2012, maturity in June 2016
Derivative
Notional amount | £		£ 7,200
Fair value of foreign currency derivative instruments not designated as hedging instruments, assets			$ 964
Effects of Change in Interest Rates
+50 Basis Points	(47)
-50 Basis Points	57
+100 Basis Points	(99)
-100 Basis Points	109
Currency swap, entered in July 2012, maturity in June 2016 | Cash flow hedge
Derivative
Semi annual buy (sell) amount			$ 11,400
Exchange rate GBP/USD		1.5695	1.5695
Currency swap, entered in January 2015, maturity in October 2017
Derivative
Notional amount | £		£ 20,000
Fair value of foreign currency hedge, assets			$ 1,505
Effects of Change in Interest Rates
+50 Basis Points	(72)
-50 Basis Points	216
+100 Basis Points	(215)
-100 Basis Points	$ 360
Currency swap, entered in January 2015, maturity in October 2017 | Cash flow hedge
Derivative
Buy (sell) amount | £		£ 1,000
Monthly buy (sell) amount			$ 30,300