Condensed Consolidating Financial Statements (Cash Flow) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net cash provided by (used in) operating activities	$ 171,687	$ 116,972
Cash flows from investing activities:
Capital expenditures	(22,053)	(11,942)
Return of capital from investees	3,908	172
Investment in and loans to investees	0	(42,318)
Payments for acquisition of a business, net of cash acquired	0
Increase (decrease) to investment in affiliates	0	0
Net cash used in investing activities	(18,145)	(54,088)
Cash flows from financing activities:
Deemed repurchases of restricted stock units	(22,959)	(15,354)
Purchase of treasury stock	(991)	(83,637)
Proceeds from stock option exercises	4,630	0
Principal payments on finance lease obligations	(1,309)	(1,406)
Distributions to noncontrolling interests	(5,629)	(1,435)
Proceeds from the issuance of long-term debt	2,521	0
Principal payments on long-term debt	(3,238)	0
Payments for financing costs		0
Net cash used in financing activities	(26,975)	(101,832)
Net increase (decrease) in cash and cash equivalents from operations	126,567	(38,948)
Effect of exchange rate changes on cash and cash equivalents	2,229	9,365
Cash and cash equivalents at beginning of period	554,886	558,783
Cash and cash equivalents at end of period	683,682	529,200
Eliminations
Cash flows from operating activities:
Net cash provided by (used in) operating activities	(217,930)	(264,998)
Cash flows from investing activities:
Capital expenditures	0	0
Return of capital from investees	0	0
Investment in and loans to investees	0	0
Payments for acquisition of a business, net of cash acquired	0
Increase (decrease) to investment in affiliates	183,451	203,739
Net cash used in investing activities	183,451	203,739
Cash flows from financing activities:
Deemed repurchases of restricted stock units	0	0
Purchase of treasury stock	0	0
Proceeds from stock option exercises	0
Principal payments on finance lease obligations	0	0
Distributions to noncontrolling interests	0	0
Proceeds from the issuance of long-term debt	0	0
Principal payments on long-term debt	0	0
Payments for financing costs		0
Net cash used in financing activities	0	0
Net increase (decrease) in cash and cash equivalents from operations	(34,479)	(61,259)
Effect of exchange rate changes on cash and cash equivalents	34,479	61,259
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	0	0
Parent Company
Cash flows from operating activities:
Net cash provided by (used in) operating activities	197,776	234,947
Cash flows from investing activities:
Capital expenditures	(26)	0
Return of capital from investees	0	0
Investment in and loans to investees	0	0
Payments for acquisition of a business, net of cash acquired	0
Increase (decrease) to investment in affiliates	(177,117)	(141,109)
Net cash used in investing activities	(177,143)	(141,109)
Cash flows from financing activities:
Deemed repurchases of restricted stock units	(22,959)	(15,354)
Purchase of treasury stock	(991)	(83,637)
Proceeds from stock option exercises	4,630
Principal payments on finance lease obligations	0	0
Distributions to noncontrolling interests	0	0
Proceeds from the issuance of long-term debt	0	0
Principal payments on long-term debt	0	0
Payments for financing costs		0
Net cash used in financing activities	(19,320)	(98,991)
Net increase (decrease) in cash and cash equivalents from operations	1,313	(5,153)
Effect of exchange rate changes on cash and cash equivalents	(607)	5,017
Cash and cash equivalents at beginning of period	121	320
Cash and cash equivalents at end of period	827	184
Guarantor Subsidiaries
Cash flows from operating activities:
Net cash provided by (used in) operating activities	164,138	154,495
Cash flows from investing activities:
Capital expenditures	(19,868)	(11,040)
Return of capital from investees	0	0
Investment in and loans to investees	0	0
Payments for acquisition of a business, net of cash acquired	0
Increase (decrease) to investment in affiliates	69,120	(129,821)
Net cash used in investing activities	49,252	(140,861)
Cash flows from financing activities:
Deemed repurchases of restricted stock units	0	0
Purchase of treasury stock	0	0
Proceeds from stock option exercises	0
Principal payments on finance lease obligations	(786)	(723)
Distributions to noncontrolling interests	0	0
Proceeds from the issuance of long-term debt	0	0
Principal payments on long-term debt	0	0
Payments for financing costs		0
Net cash used in financing activities	(786)	(723)
Net increase (decrease) in cash and cash equivalents from operations	212,604	12,911
Effect of exchange rate changes on cash and cash equivalents	(102,939)	(49,740)
Cash and cash equivalents at beginning of period	368,151	391,248
Cash and cash equivalents at end of period	477,816	354,419
Non- Guarantor Subsidiaries
Cash flows from operating activities:
Net cash provided by (used in) operating activities	27,703	(7,472)
Cash flows from investing activities:
Capital expenditures	(2,159)	(902)
Return of capital from investees	3,908	172
Investment in and loans to investees	0	(42,318)
Payments for acquisition of a business, net of cash acquired	0
Increase (decrease) to investment in affiliates	(75,454)	67,191
Net cash used in investing activities	(73,705)	24,143
Cash flows from financing activities:
Deemed repurchases of restricted stock units	0	0
Purchase of treasury stock	0	0
Proceeds from stock option exercises	0
Principal payments on finance lease obligations	(523)	(683)
Distributions to noncontrolling interests	(5,629)	(1,435)
Proceeds from the issuance of long-term debt	2,521	0
Principal payments on long-term debt	(3,238)	0
Payments for financing costs		0
Net cash used in financing activities	(6,869)	(2,118)
Net increase (decrease) in cash and cash equivalents from operations	(52,871)	14,553
Effect of exchange rate changes on cash and cash equivalents	71,296	(7,171)
Cash and cash equivalents at beginning of period	186,614	167,215
Cash and cash equivalents at end of period	$ 205,039	$ 174,597