Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Nonvested Stock Activity

The following table represents the nonvested stock activity for the year ended December 31, 2017:

	Number of Shares		Weighted Average Grant Date Fair Value
Nonvested shares outstanding at January 1, 2017	574,711		$	31.61
Granted	151,010		48.52
Vested	(192,463	)	28.95
Forfeited	(3,793	)	39.30
Nonvested shares outstanding at December 31, 2017	529,465		$	37.34

Summary of Shares Issued Under Employee Stock Purchase Plan

The following table represents the shares issued during 2017, 2016 and 2015 under the Employee Stock Purchase Plan:

	Number of Shares	Weighted Average Per Share Price
Shares available as of December 31, 2014	236,483
Shares issued in 2015	22,723	$	34.37
Shares issued in 2016	24,149	$	37.79
Shares issued in 2017	18,542	$	55.40
Shares available as of December 31, 2017	171,069