Summary of Fair Value of Plan Assets by Asset Category (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
UNITED KINGDOM
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	$ 33,610		$ 33,457		$ 28,629
UNITED KINGDOM | Mutual Funds | Balanced Fund
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	16,287	[1]	16,260	[2]
UNITED KINGDOM | Mutual Funds | Growth Funds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	17,149	[3]	17,060	[4]
UNITED KINGDOM | Cash
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	174		137
UNITED KINGDOM | Fair Value, Inputs, Level 1
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	174		137
UNITED KINGDOM | Fair Value, Inputs, Level 1 | Cash
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	174		137
UNITED KINGDOM | Fair value, Inputs, Level 2
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	33,436		33,320
UNITED KINGDOM | Fair value, Inputs, Level 2 | Mutual Funds | Balanced Fund
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	16,287	[1]	16,260	[2]
UNITED KINGDOM | Fair value, Inputs, Level 2 | Mutual Funds | Growth Funds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	17,149	[3]	17,060	[4]
JAPAN
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	412		537		801
JAPAN | Insurance Contracts
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	412	[5]	537	[5]
JAPAN | Fair value, Inputs, Level 2
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	412		537
JAPAN | Fair value, Inputs, Level 2 | Insurance Contracts
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	$ 412	[5]	$ 537	[5]

[1] This class comprises a diversified portfolio of global investments which seeks a balanced return between capital growth and fixed income and is allocated on a weighted average basis as follows: equities (54%), bonds (32%), other assets (5%) and cash (9%).

[2] This class comprises a diversified portfolio of global investments which seeks a balanced return between capital growth and fixed income and is allocated on a weighted average basis as follows: equities (51%), bonds (33%), other assets (8%) and cash (8%).

[3] This class comprises a diversified portfolio of global investments which seeks long-term capital growth and is allocated on a weighted average basis as follows: equities (67%), bonds (15%), other assets (8%) and cash (10%).

[4] This class comprises a diversified portfolio of global investments which seeks long-term capital growth and is allocated on a weighted average basis as follows: equities (70%), other assets (14%), bonds (9%), and cash (7%).

[5] This class represents funds invested in insurance contracts.