Fair Value Measurement (Tables)

3 Months Ended

Mar. 31, 2018

Fair Value Measurement [Abstract]

Fair Value Assets Recurring and Nonrecurring

		March 31, 2018					December 31, 2017
	Category		Carrying amount		Fair value		Carrying amount		Fair value
Fair values disclosed, recurring:
Cash and cash equivalents	Level 1	$	278,944	$	278,944	$	267,910	$	267,910
Restricted cash	Level 1		62,414		62,414		63,206		63,206
Short-term debt (note 14)	Level 2		5,861		5,861		7,018		7,018
Long-term debt (note 14)
Senior unsecured notes	Level 1		487,782		498,125		487,339		520,000
Term loans	Level 2		292,512		296,026		325,553		329,687