There are a number of studies that back up this claim. A 2008 study[0] found that 88% of journalists donate to the Democratic party. Jonathan Haidt has shown[1] that non-economics social sciences skew more than 14-1 liberal to conservative (and that universities have not always been so skewed).
For anyone who believes these statistics are not based on overt discrimination based on political viewpoint, a recent study[2] showed that discrimination by party is stronger than that of race. The study did so by reproducing a landmark study that demonstrated the existence of unconscious racial bias (the implicit association test), but instead using political indicators. They found that partisan political positions triggered implicit associations 50% stronger than that of racial biases. There is also a recent book called "Passing on the Right"[3] which provides some personal narratives of conservative academics.
If you're relying on academic knowledge to provide you a sense of reality, you're viewing reality through a lens that is biased to a 93% degree towards one political pole, and then receiving that knowledge through a media system which is biased to an 88% degree towards that same political pole.
Even if you, like me, generally believe that the liberal political position is correct, ideological conformity of this magnitude should frighten you.
[0] http://www.washingtonexaminer.com/article/130902
[1] http://heterodoxacademy.org/2015/09/14/bbs-paper-on-lack-of-...
[2] https://pcl.stanford.edu/research/2015/iyengar-ajps-group-po...
[3] https://www.insidehighered.com/news/2016/03/30/new-book-deta...