Reconciliation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Earnings Per Share Disclosure [Line Items]
Net income	$ 16,845	$ 15,546	$ 44,229	$ 28,472
Income allocated to participating securities (restricted stock)	(428)	(379)	(1,099)	(688)
Income attributable to common shareholders	$ 16,417	$ 15,167	$ 43,130	$ 27,784
Average number of common shares outstanding - basic	92,949,206	91,621,997	92,842,398	91,541,675
Dilutive effect of stock options				67	[1]
Average number of common shares outstanding - diluted	92,949,206	91,621,997	92,842,398	91,541,742
Income per common share attributable to common shareholders:
Basic	$ 0.18	$ 0.17	$ 0.46	$ 0.30
Diluted	$ 0.18	$ 0.17	$ 0.46	$ 0.30

[1] Excludes options to purchase 6,889,199 shares of common stock which were outstanding during the three months ended June 30, 2011; options to purchase 7,999,253 shares of common stock which were outstanding during the three months ended June 30, 2010; options to purchase 6,902,494 shares of common stock which were outstanding during the six months ended June 30, 2011; and options to purchase 8,016,292 shares of common stock which were outstanding during the six months ended June 30, 2010 because their inclusion would be anti-dilutive.