素来 is a slightly literary synonym of 一向 (yíxiàng) and 向来 (xiànglái). All three describe a habit or trait that holds 'from before until now'. 素来 sounds the most written/educated.
grammar
Place 素来 directly before the verb or adjective: 素来 + V/Adj. It does not take 了 because the meaning is already 'continuous habit'.
