Fast-casual restaurant Chipotle Mexican Grill (NYSE:CMG) has seen some impressive momentum recently as its turnaround under new CEO Brian Niccol takes hold. Investors are thrilled. Shares have surged 135% over the past 12 months.

The strength of the company's business was reinforced earlier this month when the fresh Mexican food company announced its fourth-quarter and full-year results. The quarter capped off a strong year that featured comparable-restaurant sales growth, robust digital sales, and more.

Here's a look back at some of the areas of Chipotle's business that investors have been impressed with.

Check out the latestĀ ChipotleĀ earnings call transcript.

Chipotle burrito, chips, and guacamole

Image source: Chipotle Mexican Grill.

1. Revenue rose 8.7%

Chipotle's revenue rose 8.7% year over year in 2018. Highlighting the company's momentum, this was on top of strong, double-digit revenue growth in 2017; Chipotle's revenue rose 14.7% in 2017.

The company benefited from both comparable-restaurant sales growth and 83 new restaurants.

2. Comparable-restaurant sales increased 4%

Chipotle's comparable-restaurant sales were up 4% year over year -- despite a tough comparison of 6.4% growth in 2017. The key metric saw particular momentum in the final quarter of the year, with comparable-restaurant sales increasing 6.1% year over year.

3. Digital sales surged 42.4%

One area in which everything seems to be going right for Chipotle is the company's digital sales. Digital sales skyrocketed 42.4% year over year in 2018, with 65.6% year-over-year growth in the fourth quarter of the year.

For the full year, digital sales impressively surpassed half a billion dollars. This meant digital sales accounted for 10.9% of the company's total revenue in 2018.

4. Restaurant-level operating margin expanded to 18.7%

Leverage from sales growth at its restaurants meant the company's operating margin expanded from 16.9% in 2017 to 18.7% in 2018.

5. Adjusted earnings per share jumped 33%

Combining Chipotle's strong revenue growth and its widened operating margin, the fast-casual food company's adjusted earnings per share increased 33% year over year in 2018 to $9.06.

6. Chipotle bought back $161 million of its own stock

Another way Chipotle boosted shareholder value in 2018 was with its share buybacks. The company spent $161 million buying back its own stock during 2018, repurchasing shares at an average price of $370 -- significantly lower than the stock's current price of about $600.

7. Expect mid-single-digit comparable-restaurant sales growth in 2019

Looking to this year, management is confident it can keep up its strong momentum. Chipotle guided for comparable-restaurant sales to increase at a mid-single-digit percentage rate year over year in 2019.

To help drive its growth, management plans to invest more in digital sales and marketing and roll out a loyalty program nationwide.