Reconciliation of Common Shareholders' Equity, Common Shares and Earnings Per Share - Reconciliation of weighted average common shares outstanding - basic to weighted average common shares outstanding - diluted (Details 2) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Stockholders Equity and Earnings Per Share [Abstract]
Weighted Average Common Shares Outstanding - Basic	38,832,659	37,575,413	38,316,324	37,417,283
Plus Outstanding Share Awards net of Share Reductions for Unrecognized Stock-Based Compensation Expense and Excess Tax Benefits:
Shares Expected to be Awarded for Stock Performance Awards Granted to Executive Officers based on Measurement Period-to-Date Performance	103,084	141,540	80,450	141,540
Underlying Shares Related to Nonvested Restricted Stock Units Granted to Employees	48,645	44,280	42,620	44,280
Nonvested Restricted Shares	18,029	31,079	14,556	31,079
Shares Expected to be Issued Under the Deferred Compensation Program for Directors	3,289	2,231	3,451	2,231
Total Dilutive Shares	173,047	219,130	141,077	219,130
Weighted Average Common Shares Outstanding - Diluted	39,005,706	37,794,543	38,457,401	37,636,413