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Credit and Other Debt Agreements - Summary of Corporate and Other Debt (Parenthetical) (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Fixed Rate of 6.44%, Balloon Due August 3, 2017 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	6.44%	6.44%
Periodic payments of interest and principal, expiry date	Aug. 03, 2017	Aug. 03, 2017
Fixed Rate of 2.80%, Balloon Due June 24, 2018 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	2.80%	2.80%
Periodic payments of interest and principal, expiry date	Jun. 24, 2018	Jun. 24, 2018
Fixed Rate of 5.85%, $50 Million Due November 30, 2018 and November 30, 2019 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.85%	5.85%
Long-Term debt maturities repayments in 2018	$ 50	$ 50
Long-Term debt maturities repayments in 2019	$ 50	$ 50
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	Jun. 24, 2019	Jun. 24, 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	Jun. 24, 2020	Jun. 24, 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	Jul. 10, 2020	Jul. 10, 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	Feb. 10, 2021	Feb. 10, 2021
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	Jun. 14, 2022	Jun. 14, 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	Feb. 10, 2023	Feb. 10, 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	Jun. 24, 2023	Jun. 24, 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	Aug. 02, 2023	Aug. 02, 2023
Quarterly payments of interest, description	90 day LIBOR plus	90 day LIBOR plus
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	Feb. 27, 2024	Feb. 27, 2024
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	Jun. 24, 2025	Jun. 24, 2025
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	Feb. 27, 2026	Feb. 27, 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	Jun. 02, 2026	Jun. 02, 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	Jun. 24, 2026	Jun. 24, 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	Jun. 27, 2027	Jun. 27, 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	Aug. 02, 2027	Aug. 02, 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	Aug. 04, 2027	Aug. 04, 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	Dec. 01, 2027	Dec. 01, 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	Jun. 02, 2028	Jun. 02, 2028
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	Feb. 27, 2029	Feb. 27, 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	Jun. 27, 2029	Jun. 27, 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	Aug. 02, 2029	Aug. 02, 2029
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	Jun. 02, 2031	Jun. 02, 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	Jun. 27, 2032	Jun. 27, 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	Aug. 02, 2032	Aug. 02, 2032
Prime or LIBOR Plus up to 1.45%, Expires April 8, 2021 [Member] | Credit Agreement [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	1.45%	1.45%
Periodic payments of interest and principal, expiry date	Apr. 08, 2021	Apr. 08, 2021
Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Periodic payments of interest and principal, expiry date	May 18, 2019	May 18, 2019
First Installment [Member] | Fixed Rate of 5.85%, $50 Million Due November 30, 2018 and November 30, 2019 [Member]
Debt Instrument [Line Items]
Periodic payments of interest and principal, expiry date	Nov. 30, 2018	Nov. 30, 2018
Second Installment [Member] | Fixed Rate of 5.85%, $50 Million Due November 30, 2018 and November 30, 2019 [Member]
Debt Instrument [Line Items]
Periodic payments of interest and principal, expiry date	Nov. 30, 2019	Nov. 30, 2019
Facility B [Member] | Premium Financing Debt Facility [Member] | Interbank Rates Plus 1.05%, Expires May 18, 2019 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	1.05%	1.05%
Facility C and D [Member] | Premium Financing Debt Facility [Member] | Interbank Rates Plus 0.55%, Expires May 18, 2019 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	0.55%	0.55%

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
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