Net Income Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Net Income Per Share
Net income	$ 8,177	$ 6,768
Average shares outstanding	14,506	13,814
Dilutive securities (in shares)	195	37
Average shares outstanding including dilutive securities	14,701	13,851
Net income per share, basic (in dollars per share)	$ 0.56	$ 0.49
Net income per share, diluted (in dollars per share)	$ 0.56	$ 0.49