Geographical Information - Revenues Based on Geographical Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenues
Revenues	$ 122,457	$ 122,315	$ 363,992	$ 354,329
United States [Member]
Revenues
Revenues	89,337	91,995	267,638	259,769
United Kingdom [Member]
Revenues
Revenues	26,060	23,000	74,215	70,186
Rest of World [Member]
Revenues
Revenues	$ 7,060	$ 7,320	$ 22,139	$ 24,374