Organization and Basis of Presentation - Summary of Acquisition Impact in Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income before income taxes and noncontrolling interests	$ 39,420	$ 36,992
Net income	32,487	37,007	$ 145,096
Net income attributable to noncontrolling interests	12,490	296
Net income available to common stockholders	$ 19,997	36,711
BPF [Member]
Income before income taxes and noncontrolling interests		36,992
Net income		37,007
Net income attributable to noncontrolling interests		296
Net income available to common stockholders		36,711
BPF [Member] | As Previously Reported [Member]
Income before income taxes and noncontrolling interests		7,946
Net income		7,980
Net income attributable to noncontrolling interests		296
Net income available to common stockholders		7,684
BPF [Member] | Retrospective Adjustments [Member]
Income before income taxes and noncontrolling interests		29,046
Net income		29,027
Net income available to common stockholders		$ 29,027