Separate Financial Information of Guarantor Subsidiaries Condensed Consolidated Statements of Cash Flows (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
OPERATING ACTIVITIES
Net Cash Provided by (Used in) Operating Activities	$ 43,469	$ 32,123
INVESTING ACTIVITIES
Purchases of Property, Plant and Equipment	(12,768)	(16,239)
Proceeds from Disposals of Property, Plant and Equipment	108	2,456
Proceeds from Principal Payments Received on Long-Term Note Receivable	828	500
Proceeds from Sale of Business	4,000	0
Issuance of Long-Term Note Receivable	0	(1,500)
Acquisition of Businesses, Net of Cash, Cash Equivalents and Restricted Cash Acquired	0	(353,535)
Purchase of Intangible Assets	(2,607)	(2,500)
Change in Investments in Subsidiaries	0	0
Loan Payments from Subsidiaries	0
Loan Payments from Parent	0
Loan (Payments) Borrowings from Subsidiaries		0
Net Cash Used in Investing Activities	(10,439)	(370,818)
FINANCING ACTIVITIES
Proceeds from Short-Term Debt	0	300,000
Repayments of Short-Term Debt	0	(300,000)
Loan Borrowings (Payments) from Parent		0
Change in Subsidiary Equity	0	0
Proceeds from Issuance of Long-term Debt	0	440,000
Payments of Long-term Debt	(30,216)	(81,262)
Payments of Debt Issuance Costs	0	(16,465)
Change in Capital Lease Obligations	7	0
Loan Payments to Parent	0
Loan Payments to Subsidiaries	0
Proceeds from Issuance of Common Stock	5,735	4,728
Dividends Paid	(11,356)	(11,204)
Net Cash (Used in) Provided by Financing Activities	(35,830)	335,797
Effect of Exchange Rate Changes on Cash, Cash Equivalents and Restricted Cash	(2,244)	1,587
Net Decrease in Cash, Cash Equivalents and Restricted Cash	(5,044)	(1,311)
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	59,051	58,550
Cash, Cash Equivalents and Restricted Cash at End of Period	54,007	57,239
Eliminations
OPERATING ACTIVITIES
Net Cash Provided by (Used in) Operating Activities	0	0
INVESTING ACTIVITIES
Purchases of Property, Plant and Equipment	0	0
Proceeds from Disposals of Property, Plant and Equipment	0	0
Proceeds from Principal Payments Received on Long-Term Note Receivable	0	0
Proceeds from Sale of Business	0
Issuance of Long-Term Note Receivable		0
Acquisition of Businesses, Net of Cash, Cash Equivalents and Restricted Cash Acquired		0
Purchase of Intangible Assets	0	0
Change in Investments in Subsidiaries	1,817	193,639
Loan Payments from Subsidiaries	(1,218)
Loan Payments from Parent	(986)
Loan (Payments) Borrowings from Subsidiaries		159,780
Net Cash Used in Investing Activities	(387)	353,419
FINANCING ACTIVITIES
Proceeds from Short-Term Debt		0
Repayments of Short-Term Debt		0
Loan Borrowings (Payments) from Parent		(159,780)
Change in Subsidiary Equity	(1,817)	(193,639)
Proceeds from Issuance of Long-term Debt		0
Payments of Long-term Debt	0	0
Payments of Debt Issuance Costs		0
Change in Capital Lease Obligations	0
Loan Payments to Parent	(1,218)
Loan Payments to Subsidiaries	986
Proceeds from Issuance of Common Stock	0	0
Dividends Paid	0	0
Net Cash (Used in) Provided by Financing Activities	387	(353,419)
Effect of Exchange Rate Changes on Cash, Cash Equivalents and Restricted Cash	0	0
Net Decrease in Cash, Cash Equivalents and Restricted Cash	0	0
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	0	0
Cash, Cash Equivalents and Restricted Cash at End of Period	0	0
Parent
OPERATING ACTIVITIES
Net Cash Provided by (Used in) Operating Activities	43,661	(555)
INVESTING ACTIVITIES
Purchases of Property, Plant and Equipment	(4,505)	(7,400)
Proceeds from Disposals of Property, Plant and Equipment	20	17
Proceeds from Principal Payments Received on Long-Term Note Receivable	0	0
Proceeds from Sale of Business	0
Issuance of Long-Term Note Receivable		0
Acquisition of Businesses, Net of Cash, Cash Equivalents and Restricted Cash Acquired		(304)
Purchase of Intangible Assets	(2,500)	(2,500)
Change in Investments in Subsidiaries	(1,817)	(193,639)
Loan Payments from Subsidiaries	1,218
Loan Payments from Parent	0
Loan (Payments) Borrowings from Subsidiaries		(159,780)
Net Cash Used in Investing Activities	(7,584)	(363,606)
FINANCING ACTIVITIES
Proceeds from Short-Term Debt		300,000
Repayments of Short-Term Debt		(300,000)
Loan Borrowings (Payments) from Parent		0
Change in Subsidiary Equity	0	0
Proceeds from Issuance of Long-term Debt		440,000
Payments of Long-term Debt	(30,000)	(81,143)
Payments of Debt Issuance Costs		(16,465)
Change in Capital Lease Obligations	0
Loan Payments to Parent	0
Loan Payments to Subsidiaries	(986)
Proceeds from Issuance of Common Stock	5,735	4,728
Dividends Paid	(11,356)	(11,204)
Net Cash (Used in) Provided by Financing Activities	(36,607)	335,916
Effect of Exchange Rate Changes on Cash, Cash Equivalents and Restricted Cash	143	(68)
Net Decrease in Cash, Cash Equivalents and Restricted Cash	(387)	(28,313)
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	18,469	38,484
Cash, Cash Equivalents and Restricted Cash at End of Period	18,082	10,171
Guarantor Subsidiaries
OPERATING ACTIVITIES
Net Cash Provided by (Used in) Operating Activities	219	798
INVESTING ACTIVITIES
Purchases of Property, Plant and Equipment	(58)	0
Proceeds from Disposals of Property, Plant and Equipment	0	0
Proceeds from Principal Payments Received on Long-Term Note Receivable	0	0
Proceeds from Sale of Business	0
Issuance of Long-Term Note Receivable		0
Acquisition of Businesses, Net of Cash, Cash Equivalents and Restricted Cash Acquired		0
Purchase of Intangible Assets	0	0
Change in Investments in Subsidiaries	0	0
Loan Payments from Subsidiaries	0
Loan Payments from Parent	0
Loan (Payments) Borrowings from Subsidiaries		0
Net Cash Used in Investing Activities	(58)	0
FINANCING ACTIVITIES
Proceeds from Short-Term Debt		0
Repayments of Short-Term Debt		0
Loan Borrowings (Payments) from Parent		0
Change in Subsidiary Equity	0	0
Proceeds from Issuance of Long-term Debt		0
Payments of Long-term Debt	0	0
Payments of Debt Issuance Costs		0
Change in Capital Lease Obligations	0
Loan Payments to Parent	0
Loan Payments to Subsidiaries	0
Proceeds from Issuance of Common Stock	0	0
Dividends Paid	0	0
Net Cash (Used in) Provided by Financing Activities	0	0
Effect of Exchange Rate Changes on Cash, Cash Equivalents and Restricted Cash	0	0
Net Decrease in Cash, Cash Equivalents and Restricted Cash	161	798
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	507	226
Cash, Cash Equivalents and Restricted Cash at End of Period	668	1,024
Non-Guarantor Subsidiaries
OPERATING ACTIVITIES
Net Cash Provided by (Used in) Operating Activities	(411)	31,880
INVESTING ACTIVITIES
Purchases of Property, Plant and Equipment	(8,205)	(8,839)
Proceeds from Disposals of Property, Plant and Equipment	88	2,439
Proceeds from Principal Payments Received on Long-Term Note Receivable	828	500
Proceeds from Sale of Business	4,000
Issuance of Long-Term Note Receivable		(1,500)
Acquisition of Businesses, Net of Cash, Cash Equivalents and Restricted Cash Acquired		(353,231)
Purchase of Intangible Assets	(107)	0
Change in Investments in Subsidiaries	0	0
Loan Payments from Subsidiaries	0
Loan Payments from Parent	986
Loan (Payments) Borrowings from Subsidiaries		0
Net Cash Used in Investing Activities	(2,410)	(360,631)
FINANCING ACTIVITIES
Proceeds from Short-Term Debt		0
Repayments of Short-Term Debt		0
Loan Borrowings (Payments) from Parent		159,780
Change in Subsidiary Equity	1,817	193,639
Proceeds from Issuance of Long-term Debt		0
Payments of Long-term Debt	(216)	(119)
Payments of Debt Issuance Costs		0
Change in Capital Lease Obligations	7
Loan Payments to Parent	1,218
Loan Payments to Subsidiaries	0
Proceeds from Issuance of Common Stock	0	0
Dividends Paid	0	0
Net Cash (Used in) Provided by Financing Activities	390	353,300
Effect of Exchange Rate Changes on Cash, Cash Equivalents and Restricted Cash	(2,387)	1,655
Net Decrease in Cash, Cash Equivalents and Restricted Cash	(4,818)	26,204
Cash, Cash Equivalents and Restricted Cash at Beginning of Period	40,075	19,840
Cash, Cash Equivalents and Restricted Cash at End of Period	$ 35,257	$ 46,044