Consolidated Statements of Shareholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Dividends accrued per share	$ 1.04	$ 1.02	$ 1.00
Retained Earnings [Member]
Dividends accrued per share	$ 1.04	$ 1.02	$ 1.00