Share-Based Compensation Plan (Tables)

6 Months Ended

Jun. 30, 2015

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

Summary of service condition restricted share activity

The following table provides a summary of service condition restricted share activity as of June 30, 2015:

	Shares		Weighted-Average Grant Date Fair Value
Unvested at January 1, 2015	129,988		$	27.17
Granted	40,507		$	48.87
Vested	(50,827	)	$	25.70
Forfeited	(990	)	$	36.45
Unvested at June 30, 2015	118,678		$	35.13

Performance-based Equity Awards Methodology and Assumptions

The grant date fair value of the performance awards were determined using a Monte Carlo simulation method with the following assumptions:

Performance Award Grant Date		Percentage of Total Award	Grant Date Fair Value by Component ($ in millions)	Volatility	Interest Rate	Dividend Yield
February 8, 2012
	Relative Total Shareholder Return	30.00%	$0.7	33.00%	0.34%	2.20%
	Absolute Total Shareholder Return	30.00%	$0.6	33.00%	0.34%	2.20%
	EBITDA Comparison	40.00%	$0.7	33.00%	0.34%	2.20%
January 30, 2013
	Relative Total Shareholder Return	30.00%	$0.7	31.00%	0.41%	2.20%
	Absolute Total Shareholder Return	30.00%	$0.5	31.00%	0.41%	2.20%
	EBITDA Comparison	40.00%	$0.7	31.00%	0.41%	2.20%
December 13, 2013
	Relative Total Shareholder Return	50.00%	$4.7	29.00%	0.34% - 2.25%	2.40%
	Absolute Total Shareholder Return	50.00%	$2.9	29.00%	0.34% - 2.25%	2.40%
February 4, 2014
	Relative Total Shareholder Return	30.00%	$0.7	29.00%	0.62%	2.40%
	Absolute Total Shareholder Return	30.00%	$0.5	29.00%	0.62%	2.40%
	EBITDA Comparison	40.00%	$0.8	29.00%	0.62%	2.40%
February 11, 2015
	Relative Total Shareholder Return	30.00%	$0.9	22.00%	1.02%	2.50%
	Absolute Total Shareholder Return	40.00%	$0.7	22.00%	1.02%	2.50%
	EBITDA Comparison	30.00%	$0.7	22.00%	1.02%	2.50%