Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Summary of earnings per share
Net income	$ 12,252	$ 12,183
Weighted Average Shares (in shares)
BASIC SHARES	22,823,753	21,561,006
EFFECT OF DILUTIVE SECURITIES	46,040	24,481
DILUTIVE SHARES	22,869,793	21,585,487
NET INCOME PER SHARE (in dollars per share)
BASIC EPS	$ 0.54	$ 0.57
EFFECT OF DILUTIVE SECURITIES		$ (0.01)
DILUTIVE EPS	$ 0.54	$ 0.56