Equity and Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			$ 1,719,709	$ 1,429,517
Other comprehensive income (loss) before reclassifications			3,947	12,753
Amounts reclassified from accumulated other comprehensive income (loss)			(81)	248
Total other comprehensive income (loss)	$ (11,186)	$ (815)	3,866	13,001
Ending balance	1,770,158	1,551,813	1,770,158	1,551,813
Defined Benefit Pension
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			6,303	1,138
Other comprehensive income (loss) before reclassifications			0	0
Amounts reclassified from accumulated other comprehensive income (loss)			(81)	248
Total other comprehensive income (loss)			(81)	248
Ending balance	6,222	1,386	6,222	1,386
Foreign Currency Translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			16,216	5,124
Other comprehensive income (loss) before reclassifications			3,947	12,753
Amounts reclassified from accumulated other comprehensive income (loss)			0	0
Total other comprehensive income (loss)			3,947	12,753
Ending balance	20,163	17,877	20,163	17,877
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			22,519	6,262
Ending balance	$ 26,385	$ 19,263	$ 26,385	$ 19,263