Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share [Abstract]
Net income	$ 10,492	$ 9,968
Basic-weighted average shares outstanding	28,127,000	28,029,000
Effect of dilutive potential securities	373,000	455,000
Diluted- weighted average shares outstanding	28,500,000	28,484,000
Basic (per share)	$ 0.37	$ 0.36
Diluted (per share)	$ 0.37	$ 0.35
Shares excluded from computation of earnings per share	300,000	400,000