Share-based payments (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of the restricted common stock award/unit activity

A summary of the restricted common stock award activity during the year ended December 31, 2018 is presented below:

	Shares		Weighted-Average Grant-Date Fair Value per Share ($)
Nonvested balance at January 1, 2018	143,964		39.89
Adjustment for performance-based shares	94,851		39.41
Vested	(100,479	)	38.27
Forfeited	(18,060	)	39.04
Nonvested balance at December 31, 2018	120,276		40.99

A summary of the restricted common stock unit activity during the year ended December 31, 2018 is presented below:

	Units		Weighted-Average Grant-Date Fair Value per Share ($)
Nonvested balance at January 1, 2018	19,664		38.14
Granted	110,564		43.39
Vested	(2,975	)	38.64
Forfeited	(3,412	)	43.59
Nonvested balance at December 31, 2018	123,841		42.67