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, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share Reconciliation [Abstract]
Weighted average number of common shares outstanding used in computing basic earnings per share									45,780	45,202	44,146
Add: Assumed exercise of stock options and stock awards									1,119	1,511	1,400
Weighted average number of common shares outstanding used in computing diluted earnings per share									46,899	46,713	45,546
Net income attributable to common stockholders	$ 4,075	$ 8,553	$ 6,653	$ 4,871	$ 3,115	$ 9,957	$ 17,981	$ 19,684	$ 24,152	$ 50,737	$ 76,733
Diluted earnings per share attributable to common stockholders	$ 0.09	$ 0.18	$ 0.14	$ 0.10	$ 0.07	$ 0.21	$ 0.37	$ 0.42	$ 0.51	$ 1.09	$ 1.68