Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

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

Schedule of Share-based Compensation, Equity Instruments Other Than Options, Activity

The table below summarizes award activity.

	Year Ended December 31
	2017				2016				2015
	Number of Awards		Weighted average grant-date fair value		Number of Awards		Weighted average grant-date fair value		Number of Awards		Weighted average grant-date fair value
Outstanding at beginning of period	1,040,569		$	9.97	1,157,659		$	7.52	1,406,550		$	6.21
Granted	243,940		17.52		314,060		15.47		390,200		9.61
Converted	(320,810	)	9.47		(329,200	)	7.32		(498,491	)	5.97
Expired	(82,050	)	9.22		(92,750	)	7.44		(126,800	)	5.52
Forfeited	(7,800	)	13.55		(9,200	)	10.23		(13,800	)	7.36
Outstanding at end of period	873,849		$	12.30	1,040,569		$	9.97	1,157,659		$	7.52
Vested	441,424		$	7.61	472,294		$	6.60	511,109		$	6.03

Schedule of Share-based Payment Award, Equity Instruments Other Than Options, Valuation Assumptions

The market condition awards were valued using a Monte Carlo simulation technique based on volatility over three years for the awards granted in 2017, 2016 and 2015 using daily stock prices and using the following variables:

	2017	2016	2015
Risk-free interest rate	1.7%	1.1%	0.9%
Volatility	34.7%	36.9%	41.5%