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Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands | Total | Common Stock | Additional Paid-In Capital | Retained Earnings | Accumulated Other Comprehensive Loss | Treasury Stock
--- | --- | --- | --- | --- | --- | ---
Balance, shares at Dec. 31, 2016 |  | 32,085,000 |  |  |  | 530,000
Balance at Dec. 31, 2016 | $ 460,880 | $ 320 | $ 264,418 | $ 211,748 | $ (7,721) | $ (7,885)
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |
Net income | 62,560 |  |  | 62,560 |  |
Foreign currency translation adjustment | 3,150 |  |  |  | 3,150 |
Adjustment to post-retirement healthcare benefit liability, net of taxes | 205 |  |  |  | 205 |
Stock compensation expense | 7,122 |  | 7,122 |  |  |
Net settlement of restricted stock units, shares |  | 203,000 |  |  |  | 85,000
Net settlement of restricted stock units | $ (2,872) | $ 3 | (3) |  |  | $ (2,872)
Issuance of restricted stock, shares |  | 2,000 |  |  |  |
Stock options exercised, shares | 42,058 | 42,000 |  |  |  |
Stock options exercised | $ 674 |  | 674 |  |  |
Balance, shares at Dec. 31, 2017 |  | 32,332,000 |  |  |  | 615,000
Balance at Dec. 31, 2017 | 531,719 | $ 323 | 271,957 | 274,562 | (4,366) | $ (10,757)
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |
Net income | 63,809 |  |  | 63,809 |  |
Foreign currency translation adjustment | (3,241) |  |  |  | (3,241) |
Adjustment to post-retirement healthcare benefit liability, net of taxes | 723 |  |  |  | 723 |
Stock compensation expense | 9,189 |  | 9,189 |  |  |
Net settlement of restricted stock units, shares |  | 460,000 |  |  |  | 181,000
Net settlement of restricted stock units | (7,165) | $ 5 | (5) |  |  | $ (7,165)
Issuance of restricted stock, shares |  | 7,000 |  |  |  |
Stock options exercised, shares |  | 88,000 |  |  |  |
Stock options exercised | 1,385 | $ 1 | 1,384 |  |  |
Balance, shares at Dec. 31, 2018 |  | 32,887,000 |  |  |  | 796,000
Balance at Dec. 31, 2018 | 596,693 | $ 329 | 282,525 | 338,995 | (7,234) | $ (17,922)
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |
Net income | 65,091 |  |  | 65,091 |  |
Foreign currency translation adjustment | 1,766 |  |  |  | 1,766 |
Adjustment to post-retirement healthcare benefit liability, net of taxes | 77 |  |  |  | 77 |
Stock compensation expense | 12,570 |  | 12,570 |  |  |
Net settlement of restricted stock units, shares |  | 255,000 |  |  |  | 110,000
Net settlement of restricted stock units | $ (4,305) | $ 3 | (3) |  |  | $ (4,305)
Issuance of restricted stock, shares |  | 8,000 |  |  |  |
Stock options exercised, shares | 42,350 | 42,000 |  |  |  |
Stock options exercised | $ 490 |  | 490 |  |  |
Balance, shares at Dec. 31, 2019 |  | 33,192,000 |  |  |  | 906,000
Balance at Dec. 31, 2019 | $ 673,964 | $ 332 | $ 295,582 | $ 405,668 | $ (5,391) | $ (22,227)

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