Fair Value Measurements - Narrative (Details) - USD ($) $ in Thousands, shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Jun. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Stock based compensation awards, fair value of awards outstanding		$ 47,900		$ 47,900
Deferred compensation arrangements, liability, noncurrent		37,700		37,700
YP Acquisition
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Shares held in escrow (in shares)							1.8
Number of shares expected to be returned by the seller	0.9		0.9
Amount to be paid before allowance of tax credit	$ 8,000		$ 8,000
Indemnification Asset | Fair Value, Inputs, Level 1
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value of indemnification asset	25,600		25,600		$ 24,300
Change in fair value	400		1,200
Indemnification Asset | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value of indemnification asset	$ 0	25,911	0	25,911	$ 0	$ 29,789
Change in fair value		$ (500)	$ 0	$ (3,878)