The Company recognizes certain separately identifiable intangible assets acquired in connection with business combinations and asset acquisitions. Intangible assets consist of the following:


	June 30, 2022						December 31, 2021
(in thousands)	Gross Carrying Value		Accumulated Amortization		Net Carrying Value		Gross Carrying Value		Accumulated Amortization		Net Carrying Value
Purchased customer accounts	$	873,351	$	(80,436)	$	792,915	$	851,445	$	(54,481)	$	796,964
Distributor relationships	260,421		(6,976)		253,445		100,621		(3,814)		96,807
Software	73,357		(23,563)		49,794		41,743		(18,265)		23,478
Trade names	28,523		(5,713)		22,810		24,189		(3,583)		20,606
Carrier relationships	7,859		(1,435)		6,424		7,859		(1,247)		6,612
Totals	$	1,243,511	$	(118,123)	$	1,125,388	$	1,025,857	$	(81,390)	$	944,467

Amortization expense recorded for intangible assets was $19.2 million and $10.7 million for the three months ended June 30, 2022 and 2021, respectively, and $36.7 million and $21.3 million for the six months ended June 30, 2022 and 2021, respectively.

Refer to Note 2 for a summary of goodwill recorded in connection with business combinations during the six months ended June 30, 2022. The changes in carrying value of goodwill by Operating Group for the periods are as follows:


(in thousands)	Middle Market		Specialty		MainStreet		Medicare		Total
Balance at December 31, 2021	$	901,127	$	264,018	$	38,892	$	24,704	$	1,228,741
Goodwill of acquired businesses	—		6,865		176,176		—		183,041
Measurement period adjustments(1)	2,983		516		—		—		3,499
Balance at June 30, 2022	$	904,110	$	271,399	$	215,068	$	24,704	$	1,415,281

(1) Measurement period adjustments relating to businesses acquired in the fourth quarter of 2021 increased premiums, commissions and fees receivable by $3.7 million, increased current liabilities by $7.0 million and increased consideration by $0.2 million.