Schedule of Stockholders Equity [Table Text Block] | Common Stock Accumulated Shares Outstanding $0.01 Par Additional Pain-In Treasury Retained Other Comprehensive (in thousands) Class B Value Capital Stock Earnings Income Total Balance, December 31, 201 8 28,710 8,290 $ 458 $ 370,025 $ (245,842 ) $ 942,287 $ – $ 1,066,928 Stock options exercised and stock awards 59 – 1 1,230 – – – 1,231 Stock-based compensation related to stock options, restricted shares and employee stock purchase plan – – – 8,836 – – – 8,836 Vesting of restricted share awards – 226 2 (2,317 ) – – – (2,315 ) Issuance of common stock under employee stock purchase plan 57 – 1 1,680 – – – 1,681 Common stock repurchases (639 ) (53 ) – – (26,048 ) – – (26,048 ) Dividend Class A common stock – – – – – (3,389 ) – (3,389 ) Dividend Class B common stock – – – – – (991 ) – (991 ) Other comprehensive income – – – – – – 384 384 Net income – – – – – 37,104 – 37,104 Balance, March 31, 2019 28,187 8,463 $ 462 $ 379,454 $ (271,890 ) $ 975,011 $ 384 $ 1,083,421 Stock options exercised and stock awards 87 – – 1,745 – – – 1,745 Stock-based compensation related to stock options, restricted shares and employee stock purchase plan – – – 4,258 – – – 4,258 Vesting of restricted share awards – – – (517 ) – – – (517 ) Issuance of common stock under employee stock purchase plan – – – – – – – – Common stock repurchases (251 ) (67 ) – – (12,062 ) – – (12,062 ) Dividend Class A common stock – – – – – (3,387 ) – (3,387 ) Dividend Class B common stock – – – – – (1,050 ) – (1,050 ) Other comprehensive income – – – – – – (505 ) (505 ) Net income – – – – – 41,621 – 41,621 Balance, June 30, 2019 28,023 8,396 $ 462 $ 384,940 $ (283,952 ) $ 1,012,195 $ (121 ) $ 1,113,524 Stock options exercised and stock awards 36 – – 904 – – – 904 Stock-based compensation related to stock options, restricted shares and employee stock purchase plan – – – 2,709 – – – 2,709 Vesting of restricted share awards – – – – – – – – Issuance of common stock under employee stock purchase plan 60 – 1 1,806 – – – 1,807 Common stock repurchases (313 ) (112 ) – – (16,089 ) – – (16,089 ) Dividend Class A common stock – – – – – (3,637 ) – (3,637 ) Dividend Class B common stock – – – – – (1,124 ) – (1,124 ) Other comprehensive income – – – – – – 55 55 Net income – – – – – 39,104 – 39,104 Balance, September 30, 2019 27,806 8,284 $ 463 $ 390,359 $ (300,041 ) $ 1,046,538 $ (66 ) $ 1,137,253 Common Stock Shares Outstanding $0.01 Par Additional Paid-In Treasury Retained (in thousands) Class A Class B Value Capital Stock Earnings Total Balance, December 31, 2017 31,345 8,469 $ 454 $ 348,044 $ (120,682 ) $ 812,557 $ 1,040,373 Stock options exercised and stock awards 30 – – 766 – – 766 Stock-based compensation related to stock options, restricted shares and employee stock purchase plan – – – 7,893 – – 7,893 Vesting of restricted share awards 1 226 2 (1,621 ) – – (1,619 ) Issuance of common stock under employee stock purchase plan 41 – 1 1,353 – – 1,354 Common stock repurchases (834 ) (72 ) – – (38,137 ) – (38,137 ) Net income – – – – – 21,039 21,039 Balance, March 31, 2018 30,583 8,623 $ 457 $ 356,435 $ (158,819 ) $ 833,596 $ 1,031,669 Stock options exercised and stock awards 64 – – 1,184 – – 1,184 Stock-based compensation related to stock options, restricted shares and employee stock purchase plan – – – 5,949 – – 5,949 Vesting of restricted share awards – 1 – (128 ) – – (128 ) Common stock repurchases – (194 ) – – (7,985 ) – (7,985 ) Net income – – – – – 29,389 29,389 Balance, June 30, 2018 30,647 8,430 $ 457 $ 363,440 $ (166,804 ) $ 862,985 $ 1,060,078 Stock options exercised and stock awards 32 – – 630 – – 630 Stock-based compensation related to stock options, restricted shares and employee stock purchase plan – – – 2,008 – – 2,008 Issuance of common stock under employee stock purchase plan 43 – 1 1,576 – – 1,577 Common stock repurchases (220 ) (71 ) – – (12,107 ) – (12,107 ) Dividend Class A common stock – – – – – (3,683 ) (3,683 ) Dividend Class B common stock – – – – – (1,009 ) (1,009 ) Net income – – – – – 41,665 41,665 Balance, September 30, 2018 30,502 8,359 $ 458 $ 367,654 $ (178,911 ) $ 899,958 $ 1,089,159 |