Property and Equipment - Other Items Related to Property and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property, Plant and Equipment [Line Items]
Unamortized computer software costs	$ 48,873	$ 42,134
Amortization of capitalized software	7,912	6,180	5,624
Total depreciation expense charged to income	$ 21,504	$ 20,680	$ 20,291