Financial Commitments (Summary of Interest Expense as Reported in the Condensed Consolidated Statements of Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Debt Instrument [Line Items]
Interest on debt	$ 13,957	$ 13,363	$ 41,462	$ 38,512
Other interest	540	736	1,656	2,119
Total non-cash interest expense	3,348	3,048	9,790	8,962
Total interest expense	17,305	16,411	51,252	47,474
Convertible Notes [Member]
Debt Instrument [Line Items]
Interest on debt	1,438	1,437	4,313	4,312
Total non-cash interest expense	$ 2,734	2,490	$ 8,013	7,298
Effective interest rates	9.39%		9.39%
2017 Senior Notes [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest on debt	$ 8,594	8,594	$ 25,781	25,781
Total non-cash interest expense	$ 213	198	$ 627	584
Effective interest rates	7.13%		7.13%
2017 Credit Facility [Member] | Credit Facility [Member]
Debt Instrument [Line Items]
Interest on debt	$ 3,385	2,596	$ 9,712	6,300
Total non-cash interest expense	$ 401	$ 360	$ 1,150	$ 1,080