Employee Benefit Plans - Actual and Target Allocations of Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Document Fiscal Year Focus	2017
U.S. Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	$ 617,840	$ 562,564	$ 552,817
Defined Benefit Plan Fair Value Of Plan Assets Gross	$ 209,271	$ 382,373
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Actual plan asset allocations	100.00%	100.00%
Target plan asset allocations	100.00%
U.S. Pension Plan, Defined Benefit [Member] | Equity - Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	$ 0	$ 161,426
U.S. Pension Plan, Defined Benefit [Member] | Mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	43,272
U.S. Pension Plan, Defined Benefit [Member] | Private Placement [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	1,222	1,248
U.S. Pension Plan, Defined Benefit [Member] | Collective funds at NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	$ 352,481	$ 124,456
U.S. Pension Plan, Defined Benefit [Member] | Equity securities [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Actual plan asset allocations	57.00%	57.00%
Target plan asset allocations	58.00%
U.S. Pension Plan, Defined Benefit [Member] | Fixed income investments [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Actual plan asset allocations	33.00%	35.00%
Target plan asset allocations	35.00%
U.S. Pension Plan, Defined Benefit [Member] | Real estate funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	$ 48,294	$ 45,494
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Actual plan asset allocations	10.00%	8.00%
Target plan asset allocations	7.00%
U.S. Pension Plan, Defined Benefit [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	$ 7,794	$ 10,241
Foreign Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	175,534	148,514	159,436
Defined Benefit Plan Fair Value Of Plan Assets Gross	109,403	95,131
Foreign Pension Plan [Member] | Collective funds at NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	61,648	49,357
Foreign Pension Plan [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	28,761	34,139
Foreign Pension Plan [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	4,633	3,465
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	4,592	4,354	$ 0
Level 3 [Member] | Foreign Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	4,592	4,354
Defined Benefit Plan Fair Value Of Plan Assets Gross	4,592	4,354
Level 3 [Member] | Foreign Pension Plan [Member] | Collective funds at NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 3 [Member] | Foreign Pension Plan [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 3 [Member] | Foreign Pension Plan [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 1 [Member] | U.S. Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	3,988	211,847
Defined Benefit Plan Fair Value Of Plan Assets Gross	3,988	211,847
Level 1 [Member] | U.S. Pension Plan, Defined Benefit [Member] | Equity - Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	161,426
Level 1 [Member] | U.S. Pension Plan, Defined Benefit [Member] | Mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	43,272
Level 1 [Member] | U.S. Pension Plan, Defined Benefit [Member] | Private Placement [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	1,222	1,248
Level 1 [Member] | U.S. Pension Plan, Defined Benefit [Member] | Collective funds at NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 1 [Member] | U.S. Pension Plan, Defined Benefit [Member] | Real estate funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 1 [Member] | U.S. Pension Plan, Defined Benefit [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 1 [Member] | Foreign Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	67,469	68,807
Defined Benefit Plan Fair Value Of Plan Assets Gross	67,469	68,807
Level 1 [Member] | Foreign Pension Plan [Member] | Collective funds at NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 1 [Member] | Foreign Pension Plan [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	28,761	34,139
Level 1 [Member] | Foreign Pension Plan [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	4,633	3,465
Level 2 [Member] | U.S. Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	205,283	170,526
Defined Benefit Plan Fair Value Of Plan Assets Gross	205,283	170,526
Level 2 [Member] | U.S. Pension Plan, Defined Benefit [Member] | Equity - Domestic [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 2 [Member] | U.S. Pension Plan, Defined Benefit [Member] | Mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 2 [Member] | U.S. Pension Plan, Defined Benefit [Member] | Private Placement [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 2 [Member] | U.S. Pension Plan, Defined Benefit [Member] | Collective funds at NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 2 [Member] | U.S. Pension Plan, Defined Benefit [Member] | Real estate funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 2 [Member] | U.S. Pension Plan, Defined Benefit [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 2 [Member] | Foreign Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	37,342	21,970
Defined Benefit Plan Fair Value Of Plan Assets Gross	37,342	21,970
Level 2 [Member] | Foreign Pension Plan [Member] | Collective funds at NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 2 [Member] | Foreign Pension Plan [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 2 [Member] | Foreign Pension Plan [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	$ 0	$ 0