Income Taxes - Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Computed federal income tax expense at statutory rate of 35%									$ 10,920	$ 11,050	$ 6,943
State income taxes									698	438	397
Tax credits									(1,019)	(888)	(1,385)
Foreign tax rate differential									(3,564)	(1,958)	(2,374)
Uncertain tax positions									536	(76)	(520)
Deferred compensation insurance assets									182	(81)	(358)
Other — including the effect of graduated rates									(355)	113	566
Total income tax expense	$ 145	$ 1,842	$ 3,122	$ 2,289	$ 3,680	$ 2,489	$ 1,366	$ 1,063	$ 7,398	$ 8,598	$ 3,269