Borrowings (Convertible Senior Notes Due 2013) (Detail) (USD $)	0 Months Ended	3 Months Ended		6 Months Ended
	Mar. 07, 2008	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Convertible Note [Member]
Line of Credit Facility [Line Items]
Repurchased amount of convertible notes				$ 36,600,000
Loan agreement, number of tranches				4,000,000
Principal amount of convertible notes				35,300,000
Convertible Senior Notes Due 2013 [Member]
Line of Credit Facility [Line Items]
Debt instrument issuance amount	310,000,000
Interest rate percentage on issued debt	3.00%
Year of maturity of debt	2013
Initial conversion rate shares	14.7113
Principal amount of initial conversion rate	1,000
Accrued interest		2,400,000		2,400,000		2,700,000
Pre tax non-cash interest expense recognized in consolidated statement of operations		1,400,000	1,100,000	2,500,000	2,100,000
Annual pre-tax increase in non-cash interest expense				$ 1,900,000