Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares |
Jun. 30, 2019 |
Dec. 31, 2018 |
|---|---|---|
| Class A | ||
| Common stock, par value | $ 0.01 | $ 0.01 |
| Common stock, shares authorized | 400,000,000 | 400,000,000 |
| Common stock, shares issued | 16,473,628 | 15,280,833 |
| Common stock, shares outstanding | 15,381,099 | 14,424,558 |
| Treasury stock, shares | 1,092,529 | 856,275 |
| Class B | ||
| Common stock, par value | $ 0.01 | $ 0.01 |
| Common stock, shares authorized | 200,000,000 | 200,000,000 |
| Common stock, shares issued | 54,359,620 | 55,284,408 |
| Common stock, shares outstanding | 52,175,783 | 53,137,428 |
| Treasury stock, shares | 2,183,837 | 2,146,980 |