Summary of Fair Value of Plan Assets by Asset Category (Details) - UNITED KINGDOM - USD ($) $ in Thousands	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	$ 32,374		$ 33,610		$ 33,457
Fair Value, Inputs, Level 1
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	180		174
Fair Value, Inputs, Level 2
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	32,194		33,436
Mutual Funds | Balanced Fund
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	15,611	[1]	16,287	[2]
Mutual Funds | Balanced Fund | Fair Value, Inputs, Level 2
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	15,611	[1]	16,287	[2]
Mutual Funds | Growth Funds
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	16,583	[3]	17,149	[4]
Mutual Funds | Growth Funds | Fair Value, Inputs, Level 2
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	16,583	[3]	17,149	[4]
Cash
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	180		174
Cash | Fair Value, Inputs, Level 1
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	$ 180		$ 174

[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 (52%), bonds (24%), other assets (9%) and cash (15%).

[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 (54%), bonds (32%), other assets (5%) and cash (9%).

[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 (12%), other assets (9%) and cash (12%).

[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 (67%), other assets (15%), bonds (8%), and cash (10%).