Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2021

Share-based Payment Arrangement [Abstract]

Summary of Stock Based Compensation Expense

Stock-based compensation expense is summarized as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
(in thousands)
Stock-based compensation expense	$	7,849	$	6,492	$	15,844	$	10,113

Summary of Restricted Stock Units Activity

RSU activity, inclusive of PSUs, for the six months ended June 30, 2021 is summarized as follows: 

	Number of Shares	Weighted Average Grant Date Fair Value
Outstanding at December 31, 2020	533,185	$	106.19
Granted	96,378	$	263.58
Forfeited	(20,851)	$	129.78
Settled	(183,473)	$	123.13
Outstanding at June 30, 2021	425,239	$	133.39