Summary of Significant Accounting Pronouncements (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 321,990,000	$ 256,990,000	$ 252,022,000	$ 338,956,000
Capitalized Computer Software, Additions	10,900,000	14,000,000	7,700,000
Restructuring (gain) charges	(3,728,000)	2,181,000	109,279,000
Consolidated Construction Joint Venture [Member] | Joint Venture Consolidated [Member]
Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 105,865,000	$ 75,122,000