Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 2,116,928	$ 1,831,176	$ 1,990,239	$ 1,855,900
Other comprehensive income (loss) before reclassifications			4,135	3,745
Amounts reclassified from accumulated other comprehensive income (loss)			59	(314)
Total other comprehensive income (loss)	4,037	(74)	4,194	3,431
Balance at end of period	2,222,737	1,887,620	2,222,737	1,887,620
Unrealized Gains (Losses) on Short-term Investments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period			0
Other comprehensive income (loss) before reclassifications			168
Amounts reclassified from accumulated other comprehensive income (loss)			25
Total other comprehensive income (loss)			193
Balance at end of period	193		193
Defined Benefit Pension
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period			(4,820)	2,659
Other comprehensive income (loss) before reclassifications			0	0
Amounts reclassified from accumulated other comprehensive income (loss)			34	(314)
Total other comprehensive income (loss)			34	(314)
Balance at end of period	(4,786)	2,345	(4,786)	2,345
Foreign Currency Translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period			23,935	21,153
Other comprehensive income (loss) before reclassifications			3,967	3,745
Amounts reclassified from accumulated other comprehensive income (loss)			0	0
Total other comprehensive income (loss)			3,967	3,745
Balance at end of period	27,902	24,898	27,902	24,898
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	19,272	27,317	19,115	23,812
Total other comprehensive income (loss)	4,037	(74)	4,194	3,431
Balance at end of period	$ 23,309	$ 27,243	$ 23,309	$ 27,243