Summary of Significant Accounting Policies - Revenue From Contracts Accounted for Under Time-And-Materials (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Revenue by External Customer [Line Items]
Revenue by percent	100.00%	100.00%	100.00%
Time-and-material [Member]
Schedule of Revenue by External Customer [Line Items]
Revenue by percent	90.00%	91.00%	91.00%
Progress Billing [Member]
Schedule of Revenue by External Customer [Line Items]
Revenue by percent	8.00%	7.00%	6.00%
Percentage-of-completion [Member]
Schedule of Revenue by External Customer [Line Items]
Revenue by percent	2.00%	2.00%	3.00%