Earnings per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net Income	$ 19,138	$ 18,227	$ 38,874	$ 34,816
Weighted Average Number of Shares Outstanding, Basic	84,789	86,451	84,780	86,463
Earnings Per Share, Basic	$ 0.23	$ 0.21	$ 0.46	$ 0.40
Dilutive Securities, Effect on Basic Earnings Per Share, Including Options and Restrictive Stock Units	$ 0	$ 0	$ 0	$ 0
Incremental Common Shares Attributable to Share-based Payment Arrangements	250	328	262	339
Weighted Average Number of Shares Outstanding, Diluted	85,039	86,779	85,042	86,802
Earnings Per Share, Diluted	$ 0.23	$ 0.21	$ 0.46	$ 0.40