Stock Compensation Plans (Tables)

12 Months Ended

Dec. 31, 2015

Stock Compensation Plans

Summary of status and activity of employee and non-employee directors' nonvested stock awards

			Weighted-				Weighted-				Weighted-
			Average		ROC		Average		TSR		Average
	Restricted		Grant Date		Performance		Grant Date		Performance		Grant Date
	Stock		Fair Value		Stock		Fair Value		Stock		Fair Value
	Awards		(per share)		Awards (a)		(per share)		Awards (a)		(per share)
Nonvested as of January 1, 2015	219,831		$	18.22	77,274		$	17.91	68,570		$	20.23
Granted	112,586		21.06		25,621		20.74		24,197		21.96
Vested	(117,068	)	17.14		—		—		(13,920	)	15.31
Forfeited	(10,660	)	20.43		(25,953	)	16.52		(10,342	)	20.88
Nonvested as of December 31, 2015	204,689		$	20.28	76,942		$	19.33	68,505		$	21.74

(a)The number of shares shown for the performance stock awards is based on the target number of share awards.

Employee stock options

Stock Compensation Plans

Summary of status and activity of stock options

					Weighted-Average
			Weighted-Average		Remaining
			Exercise Price		Contractual Term	Aggregate
	Shares		(per share)		(in years)	Intrinsic Value
Outstanding as of January 1, 2015	890,217		$	17.99	5.32	$	2,742
Granted	482,166		20.86
Exercised	(62,702	)	15.89
Forfeited	(46,920	)	20.97
Expired	(10,625	)	18.89
Outstanding as of December 31, 2015	1,252,136		$	19.08	5.01	$	645
Vested and expected to vest as of December 31, 2015	1,252,136		$	19.08	5.01	$	645
Exercisable as of December 31, 2015	650,877		$	17.33	4.12	$	645

Schedule of assumptions used to calculate fair values of employee stock option grants

	Year Ended December 31
	2015		2014		2013
Weighted-average grant date fair value per stock option	$	3.30	$	4.48	$	4.51
Expected dividend yield	0.96%		0.00%		0.00%
Expected volatility	19%		21 — 22%		31%
Risk-free interest rates	1.48%		1.51 — 1.73%		0.78%
Expected lives of options	4 years		4 years		4 years

Total Stockholder Return | Performance stock awards

Stock Compensation Plans

Schedule of significant assumptions used for performance stock awards

	Year Ended December 31
	2015	2014	2013
Dividend yield	0.96%	0.00%	0.00%
Expected volatility	25.9%	31.5%	37.8%
Risk-free interest rates	0.93%	0.68%	0.34%
Performance period	3 years	3 years	3 years

Directors | Non employee stock options

Stock Compensation Plans

Summary of status and activity of stock options

					Weighted-Average
			Weighted-Average		Remaining
			Exercise Price		Contractual Term	Aggregate
	Shares		(per share)		(in years)	Intrinsic Value
Outstanding as of January 1, 2015	51,255		$	6.76	1.61	$	664
Granted	—		—
Exercised	(11,370	)	5.97
Forfeited	—		—
Expired	—		—
Outstanding as of December 31, 2015	39,885		$	6.99	0.81	$	379
Vested as of December 31, 2015	39,885		$	6.99	0.81	$	379
Exercisable as of December 31, 2015	39,885		$	6.99	0.81	$	379