Fair Value - Quantitative Disclosure for Assets Classified as Level 3 (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Balance at December 31, 2014	$ 10,530
Gains included in net income	46
Gains (losses) included in comprehensive income	(36)
Investments and capital calls	377
Distributions received	(221)
Transfers into and out of Level 3	0
Balance at March 31, 2015	10,696
Limited Partnership Interests Carried at Net Asset Value
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Balance at December 31, 2014	5,380
Gains included in net income	42
Gains (losses) included in comprehensive income	0
Investments and capital calls	77
Distributions received	(221)
Transfers into and out of Level 3	0
Balance at March 31, 2015	5,278
Limited Partnership Interests Carried at Equity Method
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Balance at December 31, 2014	4,203
Gains included in net income	4
Gains (losses) included in comprehensive income	0
Investments and capital calls	0
Distributions received	0
Transfers into and out of Level 3	0
Balance at March 31, 2015	4,207
Common Stock at Fair Value
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Balance at December 31, 2014	947
Gains included in net income	0
Gains (losses) included in comprehensive income	(36)
Investments and capital calls	300
Distributions received	0
Transfers into and out of Level 3	0
Balance at March 31, 2015	$ 1,211