Enterprise-Wide Disclosures - (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 419,036		$ 424,415		$ 396,275
Total foreign revenue	77,645		69,393		67,853
Long-lived assets	8,241		6,916		7,969
Deferred tax assets, net of valuation allowance	8,669		8,485		8,368
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	341,391		355,022		328,422
Long-lived assets	7,169		6,102		7,119
Deferred tax assets, net of valuation allowance	8,669		8,485		8,368
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	1,072		814		850
Deferred tax assets, net of valuation allowance	0		0		0
Belgium [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	48,428	[1]	41,957	[1]	43,011	[1]
Other European Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	28,684		26,653		23,969
Other Country [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	533		783		873
Deferred tax assets, net of valuation allowance	$ 0		$ 0		$ 0

[1] Revenue for our Belgium operations has been disclosed separately as it exceeds 10% of consolidated revenue for certain of the years presented