Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share
Net income for basic and diluted earnings per share	$ 11,365	$ 7,715	$ 37,911	$ 21,423
Shares of common stock and common stock equivalents:
Average common shares used in basic computation	35,093	36,544	35,628	36,956
Effect of dilutive securities (in shares)	933	1,237	971	1,258
Average common shares used in diluted computation	36,026	37,781	36,599	38,214
Income per share:
Basic (in dollars per share)	$ 0.32	$ 0.21	$ 1.06	$ 0.58
Diluted (in dollars per share)	$ 0.32	$ 0.20	$ 1.04	$ 0.56
Anti-dilutive equity awards not included in the detailed earnings per share computation
Equity awards not included in the diluted earnings per share computation	471	284	421	282