Stock-Based Compensation Plans - Employee Stock Purchase Plan (Details) - Employee Stock Purchase Plan - USD ($) $ / shares in Units, shares in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock-Based Compensation Plans - Disclosures
Maximum value of company common stock that can be purchased by an employee per year	$ 25,000
Employee purchase price as a percent of fair market value (as a percent)	85.00%
Share purchases under employee stock purchase plan (in shares)	1.4	0.9	0.7
Weighted-average fair value of discount on employee stock purchase plan (in dollars per share)	$ 11.33	$ 11.37	$ 9.27
Intrinsic value from shares settled	$ 15,500,000	$ 9,700,000	$ 6,100,000
Cash received from shares issued	37,800,000	36,200,000	30,100,000
Tax benefits realized from the settlement of share-based payment arrangements	$ 900,000	$ 900,000	$ 700,000
Shares available to be issued under employee stock purchase plan (in shares)	5.0