Shareholders' Equity and Share Based Payment (Details) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Non-vested beginning balance	621,300	694,700
Granted	308,800	341,100	457,500
Cancelled	(10,600)	(69,100)	(1,500)
Vested	(268,100)	(345,400)	(322,500)
Non-vested ending balance	651,400	621,300	694,700
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments, Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Beginning Period, Weighted average grant date fair value	$ 16.15	$ 13.49	$ 12.21
Weighted average grant date fair value, Non-vested shares granted	21.58	18.80	13.98
Weighted average grant date fair value, Non-vested shares cancelled	19.22	15.89	13.11
Weighted average grant date fair value, Vested shares	15.82	13.47	11.96
Ending Period, Weighted average grant date fair value	$ 18.81	$ 16.15	$ 13.49