Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 2,058,625	$ 1,832,582	$ 1,990,239	$ 1,855,900
Other comprehensive income (loss) before reclassifications			145	3,694
Amounts reclassified from accumulated other comprehensive income (loss)			12	(189)
Total other comprehensive income (loss)	(437)	5,861	157	3,505
Balance at end of period	2,116,928	1,831,176	2,116,928	1,831,176
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			369
Amounts reclassified from accumulated other comprehensive income (loss)			(11)
Total other comprehensive income (loss)			358
Balance at end of period	358		358
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)			23	(189)
Total other comprehensive income (loss)			23	(189)
Balance at end of period	(4,797)	2,470	(4,797)	2,470
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			(224)	3,694
Amounts reclassified from accumulated other comprehensive income (loss)			0	0
Total other comprehensive income (loss)			(224)	3,694
Balance at end of period	23,711	24,847	23,711	24,847
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	19,709	21,456	19,115	23,812
Total other comprehensive income (loss)	(437)	5,861	157	3,505
Balance at end of period	$ 19,272	$ 27,317	$ 19,272	$ 27,317