Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share Reconciliation [Line Items]
Net income	$ 22,150	$ 8,457	$ 41,275	$ 19,944
Denominator for basic earnings per share - weighted-average number of common shares outstanding during the period	53,826,000	54,207,000	53,738,000	54,500,000
Incremental common shares attributable to exercise of outstanding dilutive options	443,000	205,000	461,000	213,000
Incremental common shares attributable to outstanding restricted shares and restricted stock units	136,000	88,000	195,000	184,000
Denominator for diluted earnings per share	54,405,000	54,500,000	54,394,000	54,897,000
Basic earnings per share	$ 0.41	$ 0.16	$ 0.77	$ 0.37
Diluted earnings per share	$ 0.41	$ 0.16	$ 0.76	$ 0.36
Anti-dilutive options to purchase common shares	700,000	3,200,000	700,000	3,200,000