Summary of Restricted Stock Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Restricted Shares
Restricted stock, Shares, Beginning Balance	1,817,745	1,478,000
Restricted stock, Shares, Granted	394,928	574,496
Restricted stock, Shares, Vested	(104,069)	(214,261)
Restricted stock, Shares, Cancellations	(7,550)	(3,465)
Restricted stock, Shares, Ending Balance	2,101,054	1,834,770
Fair Market Value at Date of Grant
Restricted stock, Fair Market Value at Date of Grant, Beginning Balance	$ 40,655	$ 30,600
Restricted stock, Granted, Fair Market Value at Date of Grant	10,846	15,975
Restricted stock, Vested, Fair Market Value at Date of Grant	(2,823)	(5,498)
Restricted stock, Shares, Cancellations	(157)	(72)
Restricted stock, Fair Market Value at Date of Grant, Ending Balance	$ 48,521	$ 41,005