Income Taxes - Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Computed federal income tax expense at statutory rate of 35%									$ 12,559	$ 8,885	$ 10,920
State income taxes									279	193	698
Tax credits									(1,377)	(1,164)	(1,019)
Production activity deduction									0	(53)	0
Foreign tax rate differential									(3,329)	(3,717)	(3,564)
Uncertain tax positions									(19)	597	536
Deferred compensation insurance assets									(479)	(307)	182
Transaction-related expenses									90	274	0
U.S. transition tax									10,612	0	0
TCJA remeasurement of deferred taxes									(8,383)	0	0
Share-based payments									(2,264)	0	0
Bargain purchase gain									(1,570)	0	0
In-process research and development									1,486	0	0
Other — including the effect of graduated rates									753	557	(355)
Total income tax expense	$ 4,474	$ 1,364	$ 1,830	$ 690	$ 2,116	$ (978)	$ 2,572	$ 1,555	$ 8,358	$ 5,265	$ 7,398