Goodwill and Other Intangibles - Summary of the Company’s intangible assets other than goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule of Finite and Indefinite Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 49,485	$ 48,344
Accumulated amortization, finite-lived intangible assets	(49,485)	(47,826)
Net book value	0	518
Total intangible assets at net book value	$ 900	1,418
Customer Relationships [Member]
Schedule of Finite and Indefinite Lived Intangible Assets [Line Items]
Amortization period	10 years
Finite-lived intangible assets, gross	$ 42,073	41,419
Accumulated amortization, finite-lived intangible assets	$ (42,073)	(40,901)
Internally Developed Software [Member]
Schedule of Finite and Indefinite Lived Intangible Assets [Line Items]
Amortization period	7 years
Finite-lived intangible assets, gross	$ 7,412	6,925
Accumulated amortization, finite-lived intangible assets	(7,412)	(6,925)
Trade Names [Member]
Schedule of Finite and Indefinite Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	$ 900	$ 900