Customer Concentration (Total Revenues by Geographic Area) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Concentration Risk [Line Items]
Revenues	$ 45,119	$ 67,898	$ 46,575	$ 38,518	$ 68,036	$ 62,749	$ 143,835	$ 45,440	$ 198,110	$ 320,060	$ 244,301
UNITED STATES
Concentration Risk [Line Items]
Revenues									148,622	291,448	157,327
Europe [Member]
Concentration Risk [Line Items]
Revenues									27,709	16,144	82,534
Other geographic location [Member]
Concentration Risk [Line Items]
Revenues									$ 21,779	$ 12,468	$ 4,440