Consolidated Statement Of Stockholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Issuance of common stock (in shares)	239,854	395,274	505,312
Issuance of deferred stock units (in shares)	63,677	4,784	36,578
Special cash dividend, per share	$ 2.05	$ 1.4	$ 2