Legal Proceedings - Additional Information (Details)									1 Months Ended											3 Months Ended	4 Months Ended		5 Months Ended		6 Months Ended	7 Months Ended			9 Months Ended		10 Months Ended			12 Months Ended										13 Months Ended	36 Months Ended			72 Months Ended
	Jun. 28, 2017 Plaintiff	Feb. 24, 2017 Plaintiff	May 13, 2016 case	Jan. 12, 2015 Plaintiff	Sep. 17, 2014 Plaintiff case	Nov. 30, 2012 Plaintiff	Apr. 29, 2011 USD ($)	Apr. 22, 2011 USD ($)	Nov. 30, 2017 plaintiff	Aug. 31, 2017 plaintiff Plaintiff	Dec. 31, 2016 Plaintiff	May 31, 2016 Plaintiff	Nov. 30, 2015 Plaintiff	Feb. 28, 2015 Plaintiff	Jan. 31, 2015 Plaintiff Case	Dec. 31, 2014 Plaintiff	Mar. 31, 2014 plaintiff Plaintiff	Dec. 31, 2012 Plaintiff	Nov. 30, 2011 Plaintiff	Dec. 31, 2017 USD ($)	Jul. 31, 2013 Plaintiff	Apr. 22, 2011 Plaintiff	May 31, 2016 Case	Dec. 31, 2015 Plaintiff case	Oct. 31, 2016 plaintiff Case	May 31, 2017 plaintiff	Nov. 30, 2016 plaintiff	Oct. 31, 2012 Plaintiff Case	Sep. 30, 2017 USD ($) plaintiff Plaintiff	Sep. 30, 2016	Jan. 31, 2016 Case	Nov. 05, 2015 Case	Mar. 31, 2014 case	Dec. 31, 2017 USD ($) plaintiff Plaintiff	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2013 plaintiff	Dec. 31, 2010 USD ($)	Dec. 31, 2010 plaintiff	Dec. 31, 2010 Plaintiff	Dec. 31, 2010 case	Dec. 31, 2009 USD ($) plaintiff Plaintiff case	Dec. 31, 2008 leased_unit Plaintiff	Jun. 30, 2014 case	Dec. 31, 2009 Plaintiff	Dec. 31, 2009 case	Dec. 31, 2009 Case	Dec. 31, 2004 plaintiff case	Jun. 30, 2017 USD ($)	Jan. 04, 2011 Plaintiff
Loss Contingencies [Line Items]
Number of plaintiffs																																		1,090
Gain Contingency, Unrecorded Amount | $																																																	$ 100,000
Number of plaintiffs cases dismissed						2
Reimbursement | $																																		$ 600,000	$ 200,000	$ 300,000
Settlement Agreement
Loss Contingencies [Line Items]
Claims settled amount | $																				$ 1,500,000
Chicago Firefighter Plaintiffs
Loss Contingencies [Line Items]
Number of plaintiffs		1,770
Pittsburgh Firefighter Plaintiffs | Court of Common Pleas Philadelphia County
Loss Contingencies [Line Items]
Number of plaintiffs												19
Erie County Firefighter Plaintiffs
Loss Contingencies [Line Items]
Number of plaintiffs | plaintiff																	33
Responsive Settlement Candidates
Loss Contingencies [Line Items]
Number of plaintiffs																																		717
Settlement Agreement
Loss Contingencies [Line Items]
Number of plaintiffs																						1,069
Claims settled amount | $							$ 3,800,000
Percentage of claimants agreed for settlement							93.00%	95.02%														95.02%
Percentage of claimants agreed for settlement as per settlement agreement							100.00%
Settlement Agreement payment made | $								$ 3,600,000
Circuit Court Of Cook County
Loss Contingencies [Line Items]
Number of plaintiffs | plaintiff																																																2,443
Loss Contingency, New Claims Filed, Number | case																																										6						33
Number of claimants settled																																																		308
Loss Contingency, Claims Settled and Dismissed, Number																																											27
Court of Common Pleas Philadelphia County
Loss Contingencies [Line Items]
Number of plaintiffs																																								1					71
Loss Contingency, New Claims Filed, Number | Case																																															71
Damages maximum amount | $																																						$ 100,000
Number of claimants settled																																																		1,125
Settlement Agreement payment made | $																																						$ 80,000
Loss Contingency, Claims Dismissed, Number | Case																																															3
Loss Contingency, Claims Settled and Dismissed, Number																																									2					3	4
Latvian Commercial Dispute
Loss Contingencies [Line Items]
Litigation settlement, percent of settlement costs																																			0.50
Loss contingency, loss in period | $																																			$ 1,300,000
Litigation Settlement, Percentage of Legal Fees Excluded																														50.00%
Property, Plant and Equipment, Number of Units Sold | leased_unit																																											3
Litigation Settlement, Percent of Legal Fees																														50.00%
Supreme Court of Kings County New York
Loss Contingencies [Line Items]
Loss Contingency, New Claims Filed, Number | case																																														4
Erie County Firefighter Plaintiffs | Court of Common Pleas Philadelphia County
Loss Contingencies [Line Items]
Number of plaintiffs																	61
Outside Pennsylvania Firefighter Plaintiffs | Court of Common Pleas Philadelphia County
Loss Contingencies [Line Items]
Loss Contingency, New Claims Filed, Number | Case																																2
District of Columbia Firefighter Plaintiffs | Federal Court, Eastern District of Pennsylvania
Loss Contingencies [Line Items]
Number of plaintiffs															11									193
Pennsylvania Firefighter Plaintiffs | Circuit Court Of Cook County
Loss Contingencies [Line Items]
Number of plaintiffs | plaintiff																																					74					299
Outside Chicago Firefighter Plaintiffs
Loss Contingencies [Line Items]
Number of plaintiffs	10			1,800
Outside Chicago Firefighter Plaintiffs | Circuit Court Of Cook County
Loss Contingencies [Line Items]
Number of plaintiffs | plaintiff																																																1,800
Lackawanna Firefighter Plaintiffs | Lackawanna County Pennsylvania
Loss Contingencies [Line Items]
Number of plaintiffs										70																								263
Loss Contingency, New Claims Filed, Number										5
Florida Firefighters Plaintiffs
Loss Contingencies [Line Items]
Number of plaintiffs | plaintiff																																		166
Damages maximum amount | $																													$ 75,000
Chicago Firefighter Plaintiffs
Loss Contingencies [Line Items]
Number of plaintiffs																		3	8
Chicago Firefighter Plaintiffs | Maximum
Loss Contingencies [Line Items]
Number of plaintiffs																																										40
Chicago Firefighter Plaintiffs | Minimum
Loss Contingencies [Line Items]
Number of plaintiffs | plaintiff																																										9
Chicago Firefighter Plaintiffs | Circuit Court Of Cook County
Loss Contingencies [Line Items]
Settlement Agreement payment made | $																																		$ 700								$ 400,000
New Jersey Firefighter Plaintiffs
Loss Contingencies [Line Items]
Number of plaintiffs																													89
Loss Contingency, New Claims Filed, Number | Case																							8
New Jersey Firefighter Plaintiffs | Superior Court of New Jersey, Union County
Loss Contingencies [Line Items]
Number of plaintiffs											1		34
Philadelphia Firefighter Plaintiffs | Court of Common Pleas Philadelphia County
Loss Contingencies [Line Items]
Number of plaintiffs									1	4					70	3												20	100					75					9	9
Loss Contingency, Number of Cases Scheduled | case																																												7
Loss Contingency, New Claims Filed, Number			4												2									9				20
Loss Contingency, Claims Dismissed, Number | case																																	5
New York City Firefighter Plaintiffs | Supreme Court of State of New York, New York County
Loss Contingencies [Line Items]
Number of plaintiffs														1																	235			535
Loss Contingency, New Claims Filed, Number | Case																															29
Pittsburgh Firefighter Plaintiffs | Allegheny County Pennsylvania
Loss Contingencies [Line Items]
Number of plaintiffs																					247					6	8
Loss Contingency, New Claims Filed, Number												2
Loss Contingency, Claims Dismissed, Number												55
Pittsburgh Firefighter Plaintiffs | Allegheny County Pennsylvania | Dismissed
Loss Contingencies [Line Items]
Number of plaintiffs | plaintiff																													2
Pittsburgh Firefighter Plaintiffs | Allegheny County Pennsylvania | Remaining
Loss Contingencies [Line Items]
Number of plaintiffs | plaintiff																													4
New Jersey Firefighter Plaintiffs
Loss Contingencies [Line Items]
Number of plaintiffs | plaintiff																									194									218
Loss Contingency, New Claims Filed, Number | Case																									9
Buffalo Firefighter Plaintiffs [Member] | Supreme Court of State of New York Erie County [Member]
Loss Contingencies [Line Items]
Number of plaintiffs					193
Loss Contingency, New Claims Filed, Number | case					20