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Credit and Other Debt Agreements - Summary of Corporate and Other Debt (Parenthetical) (Detail)	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Periodic payments of interest and principal, expiry date	2020	2020
Fixed Rate of 3.20%, Balloon Due June 24, 2019 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.20%		3.20%
Periodic payments of interest and principal, expiry date	2019		2019
Fixed Rate of 5.85%, balloon Due November 30, 2019 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.85%		5.85%
Periodic payments of interest and principal, expiry date	2019		2019
Fixed Rate of 3.48%, Balloon Due June 24, 2020 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.48%		3.48%
Periodic payments of interest and principal, expiry date	2020		2020
Fixed Rate of 3.99%, Balloon Due July 10, 2020 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.99%		3.99%
Periodic payments of interest and principal, expiry date	2020		2020
Fixed Rate of 5.18%, Balloon Due February 10, 2021 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.18%		5.18%
Periodic payments of interest and principal, expiry date	2021		2021
Prime or LIBOR Plus up to 1.45%, Expires June 7, 2024 [Member] | Credit Agreement [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	1.45%
Periodic payments of interest and principal, expiry date	2024
Fixed Rate of 3.69%, Balloon Due June 14, 2022 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.69%		3.69%
Periodic payments of interest and principal, expiry date	2022		2022
Fixed Rate of 5.49%, Balloon Due February 10, 2023 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.49%		5.49%
Periodic payments of interest and principal, expiry date	2023		2023
Fixed Rate of 4.13%, Balloon Due June 24, 2023 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.13%		4.13%
Periodic payments of interest and principal, expiry date	2023		2023
Floating Rate of 1.65% LIBOR Plus Balloon Due August 2, 2023 [Member]
Debt Instrument [Line Items]
Quarterly payments of interest rate	1.65%		1.65%
Periodic payments of interest and principal, expiry date	2023		2023
Quarterly payments of interest, description	90 day LIBOR plus		90 day LIBOR plus
Fixed Rate of 4.72%, Balloon due February 13, 2024 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.72%		4.72%
Periodic payments of interest and principal, expiry date	2024		2024
Fixed Rate of 4.58%, Balloon Due February 27, 2024 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.58%		4.58%
Periodic payments of interest and principal, expiry date	2024		2024
Floating Interest Rate of 1.40% LIBOR Plus Balloon Due June 13, 2024 [Member]
Debt Instrument [Line Items]
Quarterly payments of interest rate	1.40%		1.40%
Periodic payments of interest and principal, expiry date	2024		2024
Quarterly payments of interest, description	90 day LIBOR plus		90 day LIBOR plus
Fixed Rate of 4.31%, Balloon Due June 24, 2025 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.31%		4.31%
Periodic payments of interest and principal, expiry date	2025		2025
Fixed Rate of 4.85%, Balloon due February 13, 2026 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.85%		4.85%
Periodic payments of interest and principal, expiry date	2026		2026
Fixed Rate of 4.73%, Balloon Due February 27, 2026 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.73%		4.73%
Periodic payments of interest and principal, expiry date	2026		2026
Fixed Rate of 4.40%, Balloon Due June 2, 2026 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.40%		4.40%
Periodic payments of interest and principal, expiry date	2026		2026
Fixed Rate of 4.36%, Balloon Due June 24, 2026 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.36%		4.36%
Periodic payments of interest and principal, expiry date	2026		2026
Fixed Rate of 4.09%, Balloon Due June 27, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.09%		4.09%
Periodic payments of interest and principal, expiry date	2027		2027
Fixed Rate of 4.09%, Balloon Due August 2, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.09%		4.09%
Periodic payments of interest and principal, expiry date	2027		2027
Fixed Rate of 4.14%, Balloon Due August 4, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.14%		4.14%
Periodic payments of interest and principal, expiry date	2027		2027
Fixed Rate of 3.46%, Balloon Due December 1, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.46%		3.46%
Periodic payments of interest and principal, expiry date	2027		2027
Fixed Rate of 4.55%, Balloon Due June 2, 2028 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.55%		4.55%
Periodic payments of interest and principal, expiry date	2028		2028
Fixed Rate of 4.34%, Balloon due June 13, 2028 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.34%		4.34%
Periodic payments of interest and principal, expiry date	2028		2028
Fixed Rate of 5.04%, Balloon due February 13, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.04%		5.04%
Periodic payments of interest and principal, expiry date	2029		2029
Fixed Rate of 4.98%, Balloon Due February 27, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.98%		4.98%
Periodic payments of interest and principal, expiry date	2029		2029
Fixed Rate of 4.19%, Balloon Due June 27, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.19%		4.19%
Periodic payments of interest and principal, expiry date	2029		2029
Fixed Rate of 4.19%, Balloon Due August 2, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.19%		4.19%
Periodic payments of interest and principal, expiry date	2029		2029
Fixed Rate of 4.44% Balloon Due June 13, 2030 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.44%		4.44%
Periodic payments of interest and principal, expiry date	2030		2030
Fixed Rate of 5.14%, Balloon due March 13, 2031 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.14%		5.14%
Periodic payments of interest and principal, expiry date	2031		2031
Fixed Rate of 4.70%, Balloon Due June 2, 2031 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.70%		4.70%
Periodic payments of interest and principal, expiry date	2031		2031
Fixed Rate of 4.34%, Balloon Due June 27, 2032 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.34%		4.34%
Periodic payments of interest and principal, expiry date	2032		2032
Fixed Rate of 4.34%, Balloon Due August 2, 2032 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.34%		4.34%
Periodic payments of interest and principal, expiry date	2032		2032
Fixed Rate of 4.59% Balloon Due June 13, 2033 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.59%		4.59%
Periodic payments of interest and principal, expiry date	2033		2033
Fixed Rate of 5.29%, balloon due March 13, 2034 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.29%		5.29%
Periodic payments of interest and principal, expiry date	2034		2034
Fixed Rate of 4.48%, Balloon Due June 12, 2034 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.48%		4.48%
Periodic payments of interest and principal, expiry date	2034		2034
Fixed Rate of 4.69% Balloon Due June 13, 2038 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.69%		4.69%
Periodic payments of interest and principal, expiry date	2038		2038
Fixed Rate of 5.45%, balloon due March 13, 2039 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.45%		5.45%
Periodic payments of interest and principal, expiry date	2039		2039
Facility B [Member] | Interbank Rates Plus 1.05% Expires May 18, 2020 [Member] | Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	1.05%		1.05%
Facility C and D [Member] | Interbank Rates Plus 1.05% Expires May 18, 2020 [Member] | Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	0.55%		0.55%

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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