Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Accounts receivable allowance	$ 15,985	$ 14,372
Short-term finance receivables allowance	12,187	13,323
Long-term finance receivables allowance	$ 6,446	$ 7,177
Preferred stock, par value (in dollars per share)	$ 50	$ 50
Preferred stock, dividend rate	4.00%	4.00%
Preference stock, dividend (in dollars per share)	$ 2.12	$ 2.12
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, authorized (in shares)	480,000,000	480,000,000
Common stock issued (in shares)	323,337,912	323,337,912
Treasury stock (in shares)	136,734,174	137,669,194