Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share Reconciliation [Line Items]
Net income	$ 19,125	$ 11,487
Denominator for basic earnings per share - weighted-average number of common shares outstanding during the period	53,650,000	54,796,000
Incremental common shares attributable to exercise of outstanding dilutive options	436,000	215,000
Incremental common shares attributable to outstanding restricted shares and restricted stock units	191,000	139,000
Denominator for diluted earnings per share	54,277,000	55,150,000
Basic earnings per share	$ 0.36	$ 0.21
Diluted earnings per share	$ 0.35	$ 0.21
Anti-dilutive options to purchase common shares	1,000,000	3,300,000