Legal Proceedings - Additional Information (Details)											1 Months Ended													2 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									36 Months Ended	72 Months Ended
	Nov. 04, 2019 Plaintiff	Jul. 05, 2018 plaintiff Plaintiff	Feb. 05, 2018 Plaintiff	Jun. 28, 2017 Plaintiff	Feb. 24, 2017 Plaintiff	May 13, 2016 Plaintiff case	Jan. 12, 2015 Plaintiff	Sep. 17, 2014 Plaintiff case	Apr. 29, 2011 USD ($)	Apr. 22, 2011 USD ($)	Mar. 31, 2018 USD ($) Plaintiff case	Nov. 30, 2017 plaintiff	Aug. 31, 2017 Plaintiff	Dec. 31, 2016 Plaintiff	Aug. 31, 2016 plaintiff	May 31, 2016 Plaintiff	Nov. 30, 2015 Plaintiff	Feb. 28, 2015 Plaintiff	Jan. 31, 2015 case Plaintiff Case	Dec. 31, 2014 Plaintiff	Mar. 31, 2014 plaintiff Plaintiff	Dec. 31, 2012 Plaintiff	Nov. 30, 2011 Plaintiff	Sep. 30, 2017 USD ($)	Jan. 31, 2015 case	Mar. 31, 2018 USD ($)	Jul. 31, 2013 Plaintiff	Apr. 22, 2011 Plaintiff	May 31, 2016 Case	Dec. 31, 2015 Plaintiff case	Oct. 31, 2016 plaintiff Case	May 31, 2017 plaintiff	Nov. 30, 2016 plaintiff	Oct. 31, 2012 Plaintiff Case	Sep. 30, 2017 plaintiff	Jan. 31, 2016 Case	Nov. 05, 2015 Case	Dec. 31, 2019 plaintiff	Dec. 31, 2017 USD ($) plaintiff Plaintiff	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 Plaintiff	Dec. 31, 2009 Plaintiff case Case	Dec. 31, 2004 plaintiff case	Jun. 30, 2017 USD ($)	Jan. 04, 2011 Plaintiff
Loss Contingencies
Number of plaintiffs	1,320																																						1,090
Gain contingency, unrecorded amount | $																																																	$ 100,000
Settlement offer per eligible plaintiff who has already filed a lawsuit | $											$ 700
Settlement offer per eligible plaintiff who has not already filed a lawsuit | $											$ 300
Number of firefighters considered as part of the settlement	3,700
Hearing loss settlement | $																										$ 400,000
Number of plaintiffs cases dismissed																						2
Chicago Firefighter Plaintiffs
Loss Contingencies
Number of plaintiffs					1,770
Erie County Firefighter Plaintiffs
Loss Contingencies
Number of claims dismissed | plaintiff																					33
Responsive Settlement Candidates
Loss Contingencies
Number of plaintiffs																																							717
Settlement Agreement
Loss Contingencies
Number of plaintiffs																												1,069
Hearing loss settlement | $									$ 3,800,000
Percentage of claimants agreed for settlement									93.00%	95.00%																		95.00%
Percentage of claimants agreed for settlement as per settlement agreement									100.00%
Litigation settlement, amount awarded to other party | $										$ 3,600,000
Circuit Court Of Cook County
Loss Contingencies
Number of plaintiffs | plaintiff																																																2,443
Number of new claims filed | case																																													6			33
Number of claimants settled																																																		308
Number of claims settled and dismissed																																														27
Court Of Common Pleas Philadelphia County
Loss Contingencies
Number of plaintiffs																																											1				71
Number of new claims filed																																												3			71
Damages maximum amount | $																																									$ 100,000
Number of claimants settled																																																		1,125
Litigation settlement, amount awarded to other party | $																																									$ 80,000.00
Number of claims dismissed | Case																																															3
Number of claims settled and dismissed																																												2			4
Supreme Court of Kings County New York
Loss Contingencies
Number of claims dismissed | case																																															4
New York Kings County Firefighter Plaintiffs
Loss Contingencies
Number of plaintiffs			1
Erie County Firefighter Plaintiffs
Loss Contingencies
Number of plaintiffs																					61
Outside Pennsylvania Firefighter Plaintiffs | Court Of Common Pleas Philadelphia County
Loss Contingencies
Number of new claims filed | Case																																					2
District of Columbia Firefighter Plaintiffs | Federal Court, Eastern District of Pennsylvania
Loss Contingencies
Number of plaintiffs																			11											193
Number of new claims filed | case																			1
Pennsylvania Firefighter Plaintiffs | Circuit Court Of Cook County
Loss Contingencies
Number of plaintiffs | plaintiff																																								74					299
Outside Chicago Firefighter Plaintiffs
Loss Contingencies
Number of plaintiffs				10			1,800
Outside Chicago Firefighter Plaintiffs | Circuit Court Of Cook County
Loss Contingencies
Number of plaintiffs | plaintiff																																																1,800
Lackawanna Firefighter Plaintiffs | Lackawanna County Pennsylvania
Loss Contingencies
Number of plaintiffs													70																									263
Number of new claims filed													5
Florida Firefighters Plaintiffs
Loss Contingencies
Number of plaintiffs | plaintiff		166
Damages maximum amount | $																								$ 75,000
Chicago Firefighter Plaintiffs
Loss Contingencies
Number of plaintiffs																						3	8
Chicago Firefighter Plaintiffs | Maximum
Loss Contingencies
Number of plaintiffs																																													40
Chicago Firefighter Plaintiffs | Minimum
Loss Contingencies
Number of plaintiffs | plaintiff																																													9
Chicago Firefighter Plaintiffs | Circuit Court Of Cook County
Loss Contingencies
Litigation settlement, amount awarded to other party | $																																							$ 700						$ 400,000
New Jersey Firefighter Plaintiffs
Loss Contingencies
Number of plaintiffs		61
Number of new claims filed | Case																													8
New Jersey Firefighter Plaintiffs | Superior Court of New Jersey, Union County
Loss Contingencies
Number of plaintiffs														1			34
Philadelphia Firefighter Plaintiffs | Court Of Common Pleas Philadelphia County
Loss Contingencies
Number of plaintiffs		75										1			4				70	3														20					100			9	9
Number of cases scheduled | case																			7
Number of new claims filed						4													2											9				20
Number of claims dismissed						55																			5
New York City Firefighter Plaintiffs
Loss Contingencies
Number of plaintiffs		536									1
Number of new claims filed | case											1
New York City Firefighter Plaintiffs | Supreme Court of State of New York, New York County
Loss Contingencies
Number of plaintiffs																		1																		235
Number of new claims filed | Case																																				29
Pittsburgh Firefighter Plaintiffs | Allegheny County Pennsylvania
Loss Contingencies
Number of plaintiffs																19											247					6	8		4
Number of new claims filed																2
Number of claims dismissed | plaintiff																																			2
New Jersey Firefighter Plaintiffs
Loss Contingencies
Number of plaintiffs | plaintiff		218																													194
Number of new claims filed | Case																															9
Buffalo Firefighter Plaintiffs | Supreme Court of State of New York Erie County
Loss Contingencies
Number of plaintiffs								193
Number of new claims filed | case								20