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
Net income for basic and diluted earnings per share (in dollars)	$ 8,622	$ 5,458
Shares of common stock and common stock equivalents:
Average common shares used in basic computation	37,378,000	39,112,000
Effect of dilutive securities (in shares)	1,237,000	1,191,000
Average common shares used in diluted computation	38,615,000	40,303,000
Earnings per share:
Basic (in dollars per share)	$ 0.23	$ 0.14
Diluted (in dollars per share)	$ 0.22	$ 0.14
Anti-dilutive equity awards not included in the detailed earnings per share computation
Equity awards not included in the diluted earnings per share computation	1,200,000	1,200,000