Equity Method Investments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012 ventures	Mar. 31, 2011
Schedule of Equity Method Investments [Line Items]
Number of Joint Ventures	8
Equity Method Investment, Summarized Financial Information, Income Statement
Revenues	$ 83,237	$ 79,231
Gross profit	25,563	27,716
Income before provision for income taxes	19,272	19,799
Provision for income taxes	(5,968)	(6,229)
Net income	$ 13,304	$ 13,570
Japan [Member]
Schedule of Equity Method Investments [Line Items]
Number of Joint Ventures	1
Saudi Arabia [Member]
Schedule of Equity Method Investments [Line Items]
Number of Joint Ventures	1
South Korea [Member]
Schedule of Equity Method Investments [Line Items]
Number of Joint Ventures	1
United Arab Emirates [Member]
Schedule of Equity Method Investments [Line Items]
Number of Joint Ventures	1
China [Member]
Schedule of Equity Method Investments [Line Items]
Number of Joint Ventures	2
India [Member]
Schedule of Equity Method Investments [Line Items]
Number of Joint Ventures	2