If you trust the Economist [0] it's been 7.5-15K in recent years. It's very supply/demand driven, and firms tend to move in lockstep. It goes up to 100K and beyond for the senior-most non-partners. The big raise comes (like most professional services firms) in jumping from the senior-most non-partner to the junior-most partner (owner).

[0] http://www.economist.com/news/business/21636751-why-big-end-...