Summary of Operations and Significant Accounting Policies (Earnings Per Share - Diluted) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Earnings Per Share Reconciliation [Abstract]
Weighted average number of common shares outstanding used in computing basic earnings per share									45,202	44,146	42,237
Add: Assumed exercise of stock options and stock awards									1,511	1,400	1,212
Weighted average number of common shares outstanding used in computing diluted earnings per share									46,713	45,546	43,449
Net income attributable to common stockholders	$ 3,115	$ 9,957	$ 17,981	$ 19,684	$ 23,967	$ 21,162	$ 16,647	$ 14,958	$ 50,737	$ 76,733	$ 7,513
Diluted earnings per share attributable to common stockholders	$ 0.07	$ 0.21	$ 0.37	$ 0.42	$ 0.52	$ 0.46	$ 0.37	$ 0.33	$ 1.09	$ 1.68	$ 0.17