Segment Information - Financial Information by Major Geographic Area (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues:
Total revenues	$ 1,064,987	$ 953,347	$ 1,006,644
Long-lived assets:
Total long-lived assets	222,809	225,356	229,714
United States
Revenues:
Total revenues	718,538	637,482	681,827
Long-lived assets:
Total long-lived assets	130,401	132,315	141,727
United Kingdom
Revenues:
Total revenues	174,127	151,217	153,027
Long-lived assets:
Total long-lived assets	13,973	9,631	9,757
Canada
Revenues:
Total revenues	153,775	148,934	151,070
Long-lived assets:
Total long-lived assets	78,193	82,986	76,067
Other International
Revenues:
Total revenues	18,547	15,714	20,720
Long-lived assets:
Total long-lived assets	$ 242	$ 424	$ 2,163