Retirement Plans - Schedule of Plan Assets Fair Value Hierarchy (Details) (United Kingdom Subsidiary, UK Plan, USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 282,095	$ 269,811	$ 239,650
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	657	654
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	276,598	263,961
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,840	5,196
Equity and equity like investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	121,739	144,104
Equity and equity like investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Equity and equity like investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	116,899	138,908
Equity and equity like investments | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,840	5,196	4,996
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	124,380	101,337
Corporate bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	124,380	101,337
Corporate bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Government bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	35,319	23,716
Government bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Government bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	35,319	23,716
Government bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	657	654
Cash | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	657	654
Cash | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0