CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)	23,163	18,314	25,024
Issuance of common stock purchased under the Employee Stock Purchase Plan (in shares)	5,636	4,155	4,184
Forfeiture of common stock (in shares)	1,264	1,042	1,142
Release of shares of common stock under the employee stock ownership plan (in shares)	0	15,256	16,004
Cash dividends (in dollars per share)	$ 0.65	$ 0.625	$ 0.575
Purchase of common stock (in shares)	85,362	80,168	102,884