Stockholders' Equity - Summary of Transactions Relating to Common Stock (Details) - USD ($) $ in Thousands	12 Months Ended
	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