Employee Benefit Plan - Plan Assets at Fair Value (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 58,648,000	$ 60,097,000
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		58,648,000
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0	927,000
Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		115,000
Cash | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		115,000
Cash | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Cash | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Money market funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		697,000
Money market funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		697,000
Money market funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Money market funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
U.S. treasury securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		57,836,000
U.S. treasury securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		57,836,000
U.S. treasury securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
U.S. treasury securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 0