Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowances for accounts receivable	$ 6,154	$ 5,836
Accumulated amortization of operating lease	7,032
Accumulated amortization of intangibles	$ 111,520	$ 106,871
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	87,850,292	87,850,292
Treasury stock, shares (in shares)	37,699,947	37,776,659