| Year | Level | 
|---|---|
| 2004 | 188.9 | 
| 2005 | 195.3 | 
| 2006 | 201.6 | 
| 2007 | 207.342 | 
| 2008 | 215.303 | 
| 2009 | 214.537 | 
| 2010 | 218.056 | 
| 2011 | 224.939 | 
| 2012 | 229.594 | 
| 2013 | 232.957 | 
| 2014 | 236.736 | 
| 2015 | 237.017 | 
| Source: U.S. Bureau of Labor Statistics. | |