Common Stock Repurchase Programs - Additional Information (Detail) (USD $) Share data in Millions, unless otherwise specified	6 Months Ended		1 Months Ended	3 Months Ended	6 Months Ended	12 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Aug. 31, 2012 Share Repurchase Program Two Thousand And Twelve [Member]	Jun. 30, 2013 Share Repurchase Program Two Thousand And Twelve [Member]	Jun. 30, 2013 Share Repurchase Program Two Thousand And Twelve [Member]	Dec. 31, 2012 Share Repurchase Program Two Thousand And Twelve [Member]	Jun. 30, 2013 Net Share Settlement [Member]	Jun. 30, 2012 Net Share Settlement [Member]	Jun. 30, 2013 Net Share Settlement [Member]	Jun. 30, 2012 Net Share Settlement [Member]
Stock Repurchase Program [Line Items]
Repurchase of common stock, authorized amount			$ 100,000,000
Aggregate shares purchased				0.2	0.4	1.3	0.1	0.4	0.3	0.5
Aggregate purchase price	17,837,000	9,456,000		5,000,000	10,000,000	22,900,000
Value of shares surrendered to satisfy tax withholding obligations							$ 1,300,000	$ 7,800,000	$ 7,800,000	$ 9,500,000