Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Earnings Per Share Reconciliation [Abstract]
Weighted average number of common shares outstanding used in computing basic earnings per share	45,642	45,325	45,551	45,074
Net income attributable to common stockholders	$ 6,653	$ 17,981	$ 11,524	$ 37,665
Earnings per share attributable to common stockholders - basic	$ 0.15	$ 0.40	$ 0.25	$ 0.84
Weighted average number of common shares outstanding used in computing basic earnings per share	45,642	45,325	45,551	45,074
Add: Assumed exercise of stock options and stock awards	1,217	1,823	1,365	1,763
Diluted shares	46,859	47,148	46,916	46,837
Net income attributable to common stockholders	$ 6,653	$ 17,981	$ 11,524	$ 37,665
Earnings per share attributable to common stockholders - diluted	$ 0.14	$ 0.38	$ 0.25	$ 0.80