Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]
Net income	$ 11,049	$ 10,832	$ 28,589	$ 23,618
Weighted-average basic common shares outstanding	32,037,000	30,387,000	31,825,000	30,267,000
Stock options	2,727,000	2,599,000	2,649,000	2,571,000
Denominator for diluted earnings per share - Adjusted weighted-average shares	34,764,000	32,986,000	34,474,000	32,838,000
Basic	$ 0.34	$ 0.36	$ 0.90	$ 0.78
Diluted	$ 0.32	$ 0.33	$ 0.83	$ 0.72
Antidilutive securities excluded from computation of earnings per share, shares	331,000	427,000	724,000	443,000