Earnings Per Share Attributable to Stockholders (Narrative) (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Performance Share Units [Member]
Potential common share excluded from computation of diluted earnings per share (shares)	0	441,368	0	441,368
Stock Options [Member]
Potential common share excluded from computation of diluted earnings per share (shares)	853,803	28,318	426,902	1,504,394
Minimum [Member] | Performance Share Units [Member]
Number of units available for grant as a percentage of target			0.00%
Maximum [Member] | Performance Share Units [Member]
Number of units available for grant as a percentage of target			200.00%