Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2019

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,
	2019		2018		2019		2018
($ in thousands)
Stock-based compensation expense	$	5,755	$	6,164	$	11,384	$	12,073

Summary of Restricted Stock Units Activity

RSU activity for the six months ended June 30, 2019 is summarized as follows: 

	Number of Shares		Weighted Average Grant Date Fair Value
Outstanding at December 31, 2018	552,238		$	111.49
Granted	159,490		$	108.57
Forfeited	(20,589	)	$	92.98
Settled	(154,427	)	$	96.44
Outstanding at June 30, 2019	536,712		$	115.67

Summary of Stock Option Activity

Stock option activity for the six months ended June 30, 2019 is summarized as follows: 

	Number of Shares		Weighted Average Exercise Price
Outstanding at December 31, 2018	76,751		$	12.86
Exercised	(65,880	)	$	9.75
Outstanding, vested and exercisable at June 30, 2019	10,871		$	31.71