Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Operating Leases of Lessee Disclosure

Rental expense for operating leases for each of the three years ended December 31, 2017 is as follows:

	Year Ended December 31,
	2017		2016		2015
Rental expense	$	6,446	$	6,520	$	6,722

Future minimum rental commitments required under operating leases having remaining noncancelable lease terms in excess of one year at December 31, 2017 were as follows:

	Year Ended December 31,
	2018		2019		2020		2021		2022		Thereafter
Operating lease commitments	$	3,483	$	3,298	$	3,124	$	2,886	$	1,943	$	1,830

Long-term Purchase Commitment

	Year Ended December 31,
	2018		2019		2020		2021		2022		Thereafter
Purchase commitments	$	27,326	$	9,198	$	3,257	$	2,213	$	2,169	$	246,836