Capital Stock - Dividends (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash Dividends [Line Items]
Per Share Amount	$ 0.42	$ 0.42
Year 2013 [Member]
Cash Dividends [Line Items]
Per Share Amount	$ 1.395
Total	$ 4,662,000
Year 2014 [Member]
Cash Dividends [Line Items]
Per Share Amount	$ 1.92
Total	$ 38,748,000
Year 2015 [Member]
Cash Dividends [Line Items]
Per Share Amount	$ 1.68
Total	$ 41,388,000
Year 2016 [Member]
Cash Dividends [Line Items]
Per Share Amount	$ 0.56
Total	$ 18,942,000
Cumulative Total [Member]
Cash Dividends [Line Items]
Per Share Amount	$ 7.715
Total	$ 126,383,000
Subsequent Event Dividend Declaration [Member]
Cash Dividends [Line Items]
Declaration Date	4/12/2017
Payment Date	5/10/2017
Per Share Amount	$ 0.14