Commitments and Contingencies - Additional Information (Details)												1 Months Ended																		2 Months Ended	4 Months Ended	5 Months Ended		6 Months Ended	7 Months Ended		10 Months Ended		11 Months Ended	12 Months Ended								36 Months Ended			72 Months Ended
	Jul. 05, 2018 USD ($) plaintiff Plaintiff	Feb. 05, 2018 Plaintiff	Jun. 28, 2017 Plaintiff	Apr. 25, 2017 USD ($)	Feb. 24, 2017 Plaintiff	May 13, 2016 case plaintiff	Jan. 12, 2015 Plaintiff	Sep. 17, 2014 case Plaintiff	Nov. 30, 2012 Plaintiff	Apr. 29, 2011 USD ($)	Apr. 22, 2011 USD ($) Plaintiff	Mar. 31, 2018 USD ($)	Mar. 31, 2018 plaintiff	Mar. 31, 2018 Plaintiff	Nov. 30, 2017 plaintiff	Sep. 30, 2017 plaintiff	Aug. 31, 2017 Plaintiff	Dec. 31, 2016 Plaintiff	Aug. 30, 2016 plaintiff	May 31, 2016 Plaintiff	Nov. 30, 2015 Plaintiff	Feb. 28, 2015 Plaintiff	Jan. 31, 2015 case	Jan. 31, 2015 Plaintiff	Jan. 31, 2015 Case	Dec. 31, 2014 Plaintiff	Mar. 31, 2014 Plaintiff plaintiff	Dec. 31, 2012 Plaintiff	Nov. 30, 2011 Plaintiff	Sep. 30, 2017 USD ($)	Jul. 31, 2013 Plaintiff	May 31, 2016 Case	Dec. 31, 2015 Plaintiff case	Oct. 31, 2016 Case plaintiff	Nov. 30, 2016 plaintiff	Oct. 31, 2012 Plaintiff Case case	Jan. 31, 2016 Case	Nov. 05, 2015 Case	Sep. 30, 2017 plaintiff	Dec. 31, 2017 USD ($) Plaintiff plaintiff	Dec. 31, 2013 plaintiff	Dec. 31, 2010 USD ($)	Dec. 31, 2010 case	Dec. 31, 2010 plaintiff	Dec. 31, 2010 Plaintiff	Dec. 31, 2009 USD ($) Plaintiff plaintiff case	Dec. 31, 2008 Plaintiff	Dec. 31, 2009 case	Dec. 31, 2009 Plaintiff	Dec. 31, 2009 Case	Dec. 31, 2004 case plaintiff	Jun. 30, 2021 USD ($)	Jan. 04, 2011 Plaintiff
Commitments Disclosure [Line Items]
Outstanding letters of credit and bonds | $																																																				$ 34,400,000
Number of plaintiffs (plaintiff)														1,320
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
Number of plaintiffs cases dismissed (plaintiff)									2
Circuit Court Of Cook County
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff) | plaintiff																																																			2,443
Number of cases of plaintiff's claims (case)																																															27
Number of claimants settled (plaintiff)																																																					308
Number of new claims filed (case) | case																																														6					33
Court of Common Pleas, Philadelphia County
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)																																													1				71
Number of cases of plaintiff's claims (case)																																											2					3		4
Number of claims dismissed (case) | Case																																																		3
Damages maximum amount | $																																										$ 100,000
Number of claimants settled (plaintiff)																																																					1,125
Litigation settlement | $																																										$ 80,000.00
Number of new claims filed (case) | Case																																																		71
Settlement Agreement
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)											1,069
Claims settled amount | $										$ 3,800,000
Percentage of claimants agreed for settlement										93.00%	95.00%
Percentage of claimants agreed for settlement as per settlement agreement										100.00%
Litigation settlement | $											$ 3,600,000
Supreme Court of Kings County New York
Commitments Disclosure [Line Items]
Number of new claims filed (case) | case																																																4
Lackawanna Firefighter Plaintiffs | Lackawanna County Pennsylvania [Member]
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)																	70
Number of new claims filed (case)																	5
Outside Chicago Firefighter Plaintiffs
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)			10				1,800
Outside Chicago Firefighter Plaintiffs | Circuit Court Of Cook County
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff) | plaintiff																																																			1,800
Pennsylvania Firefighter Plaintiffs | Circuit Court Of Cook County
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff) | plaintiff																																									74					299
Chicago Firefighter Plaintiffs
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)									3																			3	8
Chicago Firefighter Plaintiffs | Maximum
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)																																														40
Chicago Firefighter Plaintiffs | Circuit Court Of Cook County
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)																																														9
Litigation settlement | $																																								$ 700						$ 400,000
Philadelphia Firefighter Plaintiffs | Court of Common Pleas, Philadelphia County
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)	75					55									1				4				7	70		3										20				100				9	9
Number of claims dismissed (case) | case																																				5
Number of new claims filed (case)						4																			2								9			20
District of Columbia Firefighter Plaintiffs | Federal Court, Eastern District of Pennsylvania
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)																								11									193
Number of new claims filed (case) | case																							1
Outside Pennsylvania Firefighter Plaintiffs | Court of Common Pleas, Philadelphia County
Commitments Disclosure [Line Items]
Number of new claims filed (case) | Case																																						2
Pittsburgh Firefighter Plaintiffs | Allegheny County, Pennsylvania
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)																															247				8				6
Number of claims dismissed (case)																				55
Number of new claims filed (case)																				2
Buffalo Firefighter Plaintiffs | Supreme Court of State of New York Erie County
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)								193
Number of new claims filed (case) | case								20
New York City Firefighter Plaintiffs
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)													1	1
New York City Firefighter Plaintiffs | Supreme Court of State of New York, New York County
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)	536																					1															235
Number of new claims filed (case) | Case																																					29
New York Kings County Firefighter Plaintiffs
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)		1
New Jersey Firefighter Plaintiffs
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)	61
Number of new claims filed (case) | Case																																8
New Jersey Firefighter Plaintiffs | Superior Court of New Jersey, Union County
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)																		1			34
Massachusetts Firefighter Plaintiffs
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff) | plaintiff	218																																	194
Number of new claims filed (case) | Case																																		9
Erie County Firefighter Plaintiffs | Court of Common Pleas, Philadelphia County
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)																											61
Florida Firefighters Plaintiffs
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff) | $	166
Damages maximum amount | $																														$ 75,000
Property Lease Guarantee
Commitments Disclosure [Line Items]
Guarantor obligation, single year maximum cash payments | $																																																				3,300,000
Guarantor obligation, maximum potential cash payments | $																																																				3,300,000
Property Lease Guarantee | Affiliated Entity
Commitments Disclosure [Line Items]
Guarantor obligation, maximum potential cash payments | $																																																				$ 1,900,000
Dismissed | Pittsburgh Firefighter Plaintiffs | Allegheny County, Pennsylvania
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff) | plaintiff																2
Settlement Candidates
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)																																								1,090
Chicago Firefighter Plaintiffs
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)					1,770
Erie County Firefighter Plaintiffs
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff) | plaintiff	28																										33
Responsive Settlement Candidates
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)																																								717
Remaining | Pittsburgh Firefighter Plaintiffs | Allegheny County, Pennsylvania
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff) | plaintiff																4
Court of Common Pleas, Philadelphia County | Pittsburgh Firefighter Plaintiffs
Commitments Disclosure [Line Items]
Number of plaintiffs (plaintiff)																				19