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Stockholders' Equity - Summary of Transactions Relating to Common Stock (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Common Stock Outstanding Roll Forward [Roll Forward] |  |  |
Payments for purchases of treasury stock | $ 176,302 | $ 199,042 | $ 260,832
Common Stock |  |  |
Common Stock Outstanding Roll Forward [Roll Forward] |  |  |
Beginning balance | 163,602,067 | 163,602,067 | 163,602,067
Issuances under stock plans | 0 | 0 | 0
Purchases for treasury | 0 | 0 | 0
Ending balance | 163,602,067 | 163,602,067 | 163,602,067
Treasury Stock |  |  |
Common Stock Outstanding Roll Forward [Roll Forward] |  |  |
Beginning balance | 74,444,288 | 73,899,977 | 72,779,205
Issuances under stock plans | (820,065) | (825,115) | (933,246)
Purchases for treasury | 1,135,762 | 1,369,426 | 2,054,018
Ending balance | 74,759,985 | 74,444,288 | 73,899,977

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