Business Segments Revenue and Long-Lived Assets by Geographic Location (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Net service revenues	$ 1,221,450	$ 1,224,308	$ 1,164,914	$ 1,084,342	$ 1,083,864	$ 1,075,119	$ 1,063,228	$ 1,023,684	$ 4,695,014	$ 4,245,895	$ 4,111,213
Assets, long-lived	121,754				112,644				121,754	112,644	107,680
Domestic
Segment Reporting Information [Line Items]
Net service revenues									3,623,812	3,219,820	3,022,274
Assets, long-lived	101,181				92,252				101,181	92,252	86,239
Foreign
Segment Reporting Information [Line Items]
Net service revenues									1,071,202	1,026,075	1,088,939
Assets, long-lived	$ 20,573				$ 20,392				$ 20,573	$ 20,392	$ 21,441