Revenue and Long-Lived Assets for Each of Geographic Areas (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 173,357	$ 204,824	$ 242,745	$ 236,990	$ 225,828	$ 216,909	$ 206,776	$ 182,509	$ 857,916	$ 832,022	$ 597,779
Property, Plant and Equipment	83,304				76,672				83,304	76,672	59,321
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									674,106	611,240	468,190
Property, Plant and Equipment	67,821				69,438				67,821	69,438	52,875
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									57,623	71,389	55,395
Property, Plant and Equipment	2,890				3,353				2,890	3,353	2,375
All Other Countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									126,187	149,393	74,194
Property, Plant and Equipment	$ 12,593				$ 3,881				$ 12,593	$ 3,881	$ 4,071