Comprehensive Income Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (28,235)	$ (31,213)	$ (36,482)		$ (15,521)	$ (18,853)	$ (36,482)	$ (18,853)
Other comprehensive income (loss) before reclassifications	2,862	4,437	10,021	$ 3,936	(10,758)	4,273
Amounts reclassified from AOCI to net income (loss)	2,933	(1,459)	(4,752)	(1,239)	(593)	(941)
Net current-period other comprehensive income	5,795	2,978	5,269	2,697	(11,351)	3,332	14,042	(5,322)
Balance at end of period	(22,440)	(28,235)	(31,213)	(24,175)		(15,521)	(22,440)	(24,175)
Currency translation gain (loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(31,813)	(38,570)	(43,987)		(17,753)	(19,493)	(43,987)	(19,493)
Other comprehensive income (loss) before reclassifications	2,591	6,757	5,417	2,811	(11,566)	1,740
Amounts reclassified from AOCI to net income (loss)	0	0	0	0	0	0
Net current-period other comprehensive income	2,591	6,757	5,417	2,811	(11,566)	1,740
Balance at end of period	(29,222)	(31,813)	(38,570)	(26,508)		(17,753)	(29,222)	(26,508)
Net unrealized gain (loss) on investments (net of tax)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(23)	(3)	(37)		(25)	(44)	(37)	(44)
Other comprehensive income (loss) before reclassifications	69	(19)	61	18	(7)	18
Amounts reclassified from AOCI to net income (loss)	(4)	(1)	(27)	0	0	1
Net current-period other comprehensive income	65	(20)	34	18	(7)	19
Balance at end of period	42	(23)	(3)	(14)		(25)	42	(14)
Net unrealized gain (loss) on derivative instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(1,316)	1,546	802		3,359	1,786	802	1,786
Other comprehensive income (loss) before reclassifications	268	(2,204)	4,587	1,132	778	2,576
Amounts reclassified from AOCI to net income (loss)	3,567	(658)	(3,843)	(1,247)	(651)	(1,003)
Net current-period other comprehensive income	3,835	(2,862)	744	(115)	127	1,573
Balance at end of period	2,519	(1,316)	1,546	3,371		3,359	2,519	3,371
Net unrecognized gain (loss) related to benefit plans (net of tax)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	4,917	5,814	6,740		(1,102)	(1,102)	6,740	(1,102)
Other comprehensive income (loss) before reclassifications	(66)	(97)	(44)	(25)	37	(61)
Amounts reclassified from AOCI to net income (loss)	(630)	(800)	(882)	8	58	61
Net current-period other comprehensive income	(696)	(897)	(926)	(17)	$ 95	0
Balance at end of period	$ 4,221	$ 4,917	$ 5,814	$ (1,024)		$ (1,102)	$ 4,221	$ (1,024)